have will replace has because –
The police is a Plural Noun. Hence, Plural Verb will be used.
Look at the examples given below :

Correct Option: B

have will replace has because –
The police is a Plural Noun. Hence, Plural Verb will be used.
Look at the examples given below :

has watched will replace has been watching because–
the sentence is indicating an unspecified time expression (ever, never, already, just, many times, etc.) as in –
I have seen that movie twenty times.
Present Perfect Tense will be used.
Hence, Ahmed has watched is the right usage

Correct Option: A

has watched will replace has been watching because–
the sentence is indicating an unspecified time expression (ever, never, already, just, many times, etc.) as in –
I have seen that movie twenty times.
Present Perfect Tense will be used.
Hence, Ahmed has watched is the right usage

had cleared will replace cleared because –
that action has occurred in Past (a long time ago) as in –
I had lived in America. (The sense of time in this sentence refers to a completed action in Past)
Past Perfect Tense will be used.
Hence, the fog had cleared is the right usage

Correct Option: B

had cleared will replace cleared because –
that action has occurred in Past (a long time ago) as in –
I had lived in America. (The sense of time in this sentence refers to a completed action in Past)
Past Perfect Tense will be used.
Hence, the fog had cleared is the right usage

at will replace in because –
at (Prep.) is used with Adjectives to show how well somebody does something.
Look at the examples given below :

Correct Option: B

at will replace in because –
at (Prep.) is used with Adjectives to show how well somebody does something.
Look at the examples given below :

No error.

Correct Option: D

No error.