Correct answer: D. within
Explanation:
The preposition “within” means “inside the limits of” or “in less than” a specific period of time. It emphasizes that the action (answering all questions) must be completed before the one-hour time limit is over.
The structure is: complete a task + within + [a period of time]
Why the other options are incorrect:
• A. by: This means “not later than” a specific point in time (e.g., “You must finish by 11:00 AM”). It refers to a deadline, not a duration.
• B. on: This is used for specific days and dates (e.g., “on Monday,” “on July 5th”). It is not used for a duration of time.
• C. before: This also refers to a point in time, meaning earlier than a specific moment (e.g., “You must finish before the bell rings”). Like “by,” it does not describe a time limit for the duration of the action itself.
Examples:
Please submit the report within two days.
The ambulance arrived within minutes.
All applications must be received within the deadline.
Therefore, “In the examination, you must answer all questions within an hour” correctly means you have a one-hour time limit to complete the task.

Correct answer: C. towards
Explanation:
The verb “leans” is followed by the preposition “towards” to indicate a tendency, inclination, or preference in a certain direction—whether literal (physical) or figurative (ideological).
The structure is: lean + towards + [an idea, opinion, or physical direction]
Why the other options are incorrect:
• A. with: This means “accompanied by” or “using,” which does not convey the sense of inclination or tendency.
• B. for: This indicates purpose or support (e.g., “I am for democracy”), but it is not used with the verb “lean” to express a mental or ideological tendency.
• D. None of the above: This is incorrect because option C is the correct answer.
Examples:
Politically, he leans towards socialism.
I’m leaning towards accepting the new job offer.
The tree was leaning towards the river.

Correct answer: C. at
Explanation:
The correct preposition here is “at”. We use “astonished at” to refer to the cause or reason for someone’s astonishment.

• “At” is used after “astonished” to indicate the thing or event that caused the surprise or shock. For example, “I was astonished at the sad news” means that the sad news was the cause of astonishment.
• “To” is used for direction or purpose, but not in this context of astonishment.
• “With” is typically used to indicate manner or accompaniment, not a cause of surprise.
• “In” is used to describe states or locations but is not appropriate for emotional reactions like astonishment.
Thus, “I was astonished at the sad news” is grammatically correct because “at” introduces the cause of the astonishment.

Correct answer: C. among
Explanation:
The preposition “among” is used when referring to three or more people or things. Since there are four children, “among” is the correct choice to indicate that the quarreling is happening within the group.
Why the other options are incorrect:
• A. on: This preposition is not used with “quarrel.” We quarrel about or over something, not “on” something.
• B. in: While the quarreling happens in school, the phrase “quarrel in themselves” is incorrect. The preposition needed here is the one that shows the relationship between the children.
• D. between: The preposition “between” is used for relationships involving two separate parties. Since there are four children, “among” is the appropriate preposition.
Examples:
The sweets were shared among the five girls.
There was a disagreement between the two brothers.
They were arguing among themselves.
Therefore, “These four children always quarrel among themselves in school” is grammatically correct.

Correct answer: B. at
Explanation:
The verb “aim” is followed by the preposition “at” when it means to direct one’s efforts towards a goal or target. The goal is often a noun or a gerund (a verb ending in -ing that functions as a noun).
The structure is: aim + at + [gerund/noun]
Why the other options are incorrect:
• A. to: The structure “aim to” is also correct, but it is followed by the base form of a verb (the infinitive without “to”). For example, “He aims to win a prize.” Since the sentence uses the gerund “winning,” “at” is required.
• C. on: The preposition “on” is not used with the verb “aim” in this context.
• D. for: While “aim for” can sometimes be used to talk about a desired destination (“aim for the stars”), “aim at” is more commonly used for targeting a specific achievement or action, especially when followed by a gerund.
Examples:
This program is aimed at helping young people.
She aimed at becoming a doctor.
He aims to become a doctor. (Here, “to become” is an infinitive, so “aims to” is correct.)
Therefore, “Pavan says that he aims at winning at least a consolation prize” is the grammatically correct structure because it is followed by the gerund “winning.”

Correct answer: D. to
Explanation:
The verb “adhere” means to stick firmly to something. It is followed by the preposition “to” to indicate what is being followed or obeyed strictly.
The structure is: adhere + to + [rule/plan/agreement]
Why the other options are incorrect:
• A. in: This preposition is not used with “adhere.”
• B. by: While “abide by” is a correct phrase, “adhere by” is not standard usage.
• C. on: This preposition is not used with “adhere.”
Examples:
All members must adhere to the club’s rules.
The tape should adhere to the surface smoothly.
She adheres to her principles strictly.
Therefore, “Both parties must adhere to the terms of the contract” is the grammatically correct way to state that they must follow the terms strictly.

Correct answer: C. with
Explanation:
The adjective “friendly” is followed by the preposition “with” when referring to the person or group with whom someone has a friendly relationship.
The structure is: friendly + with + [person/people]
Why the other options are incorrect:
• A. to: We use “friendly to” when referring to an act or behavior toward someone (e.g., “She was friendly to the new student”). However, when describing an ongoing relationship, “friendly with” is more appropriate.
• B. at: This preposition is not used with “friendly.”
• D. over: This preposition is not used with “friendly.”
Examples:
He is very friendly with his colleagues.
Are you friendly with your neighbors?
The dog is friendly with children.
Therefore, “You are rather friendly with the others, aren’t you?” correctly describes having a friendly relationship with the other people.

Correct answer: at
Explanation:
The verb “smiled” is followed by the preposition “at” to indicate the target or reason for the smile.
The structure is: smile + at + [person/thing]
Why the other options are incorrect:
• A. on and B. upon: These prepositions are not used with “smile” to indicate the target. “Smile upon” is an old-fashioned or literary phrase meaning to regard with favor (e.g., “Fortune smiled upon him”), but it is not used for reacting to a specific thing like a mistake.
• C. over: This can mean “because of” or “during,” (e.g., “We laughed over the incident”), but it is less direct and common than “at” for a simple reaction like a smile.
Examples:
She smiled at the child.
He smiled at her joke.
Why are you smiling at me?
Therefore, “She smiled at my mistakes” is the correct and natural way to say that my mistakes were the reason for her smile.

Correct answer: B. for
Explanation:
The correct preposition here is “for”. We use “bargain for” when referring to something that was not anticipated or expected.

• “Bargain for” is a phrasal verb used to express something that one has not anticipated or expected. For example, “We did not exactly bargain for him turning up like that” means we did not expect or plan for him to arrive in that manner.
• “About” is used to discuss topics or subjects but doesn’t fit in the context of unexpected events.
• “Of” is typically used for possession or characteristics, not for bargaining.
• “To” is used for direction or purpose, but not in the context of negotiating or expecting something.
Thus, “We did not exactly bargain for him turning up like that out of the blue” is correct because “for” expresses the unexpected nature of the situation.

Correct answer: to
Explanation:
The adjective “responsible” can be followed by different prepositions depending on the meaning.
1. Responsible to: This is used to indicate the person or authority to whom one must answer or report.
Structure: responsible + to + [person/authority]
2. Responsible for: This is used to indicate the thing, task, or person that one is in charge of or obligated to manage.
Structure: responsible + for + [thing/task/person]
Analyze the sentence:
• “He” must answer or report to “the president.”
• He is accountable for “his decisions.”
The sentence structure shows the chain of accountability: He (is responsible) → [to the president] → [for his decisions].
Why the other options are incorrect:
• A. for: Using “for” would create the incorrect phrase “responsible for the president,” which would mean he is in charge of the president, which is not the intended meaning.
• B. of: This is not the standard preposition used with “responsible.”
• D. with: This preposition is not used with “responsible.”
Examples:
Managers are responsible to the board of directors for the company’s performance.
She is responsible to her boss for completing the project.
Therefore, “He is responsible to the president for his decisions” is the grammatically correct structure.