Explanation

Life promises a lot of pleasure.

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a lot of (Idiom): a large number or amount of somebody/ something

Here, of is the right usage.

because "of" is the preposition used to show somebody/something belongs to a group (a lot of pleasure)

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Explanation

Generally grateful is followed by for.

Grateful for something means کسی چیز کیلئے احسان مند ہونا

Grateful to someone means کسی انسان کا احسان مند ہونا

They are very grateful for your kindness. 

Explanation

Generally prefer is followed by To.

To is a preposition here.

Prefer means ترجیع دینا

I prefer to go by air. 

Explanation

The District Police Officer is invested with Magistrate Powers. 

We use preposition with to show additional powers of someone. 

Explanation

"Before entering" is the correct phrase, indicating the action should happen prior to entering.

It properly links with the verb "ask permission" to show timing and respect.

Explanation

"Through" is used when something passes in one side and out the other of an opening, like a window.

So, "through the window" correctly describes how the fumes were entering the van.

Explanation

The correct preposition used with "expertise" is "in" when referring to a subject or field.

So, "He has expertise in the famous world language" is grammatically correct.

Explanation

In can be used in the following ways: as a preposition (followed by a noun): The children are in the garden. 

As an adverb (without a following noun): Come in and sit down.

Explanation

He has no trust in his own skill. 

Trust in something means کسی چیز پر اعتماد ہونا

Explanation

We use “on” with days and dates (e.g., on Monday, on Friday, on July 5).
This sentence refers to a specific day, so:  “On Friday” is correct.