Explanation

 The subject is "One", which is singular.

"Of the boys" is a prepositional phrase and does not affect the verb.

Explanation

For is used for period.

Since is used for point of time.

He has eaten nothing for a long time means اس نے کافی عرصے سے کچھ نہیں کھایا

Explanation

He applied for the job. 

اس نے نوکری کے لیے اپلائی کیا۔

The verb "apply" is commonly followed by the preposition "for" when referring to a request for something

Explanation

'At' indicates specific time, location or position.

Hence it is the correct preposition to be used in the sentence.

Explanation

Generally oppose is followed by To.

Oppose means مخالفت کرنا

We opposite to policy of yours. 

Explanation

The supervisor thought on the most suitable person to do the job 

Explanation

At is used for precise time.

The shop closes at mid-night. 

Explanation

Difficulty in doing something makes sense.

In finding the house means مکان کو تلاش کرنے میں

Explanation

Bananas are selling at Rs 250 per dozen.

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Explanation

He scoffed at the idea of revolution

Here, at denotes the position in which he scoffed.

So, "at" is right here.