Explanation:

The original sentence is incorrect

Reason: There are two errors in the bold part.

Firstly, the term ‘police’ is a collective noun. Collective nouns are used in singular form. Therefore, ‘polices’ must be replaced by ‘police’ in order to make the sentence correct.

Secondly, ‘hardly’ and ‘when’ form a pair of coordinating conjunctions. Coordinating conjunctions join phrases, words, etc. of equal ranks. Therefore, ‘when’ should be used instead of ‘than’ in order to make it a grammatically correct sentence.

Among the choices available, option C replaces the bold part most appropriately.

The sentence after replacement becomes:

Hardly had the thieves seen the police when they started running towards the black van.

Option C is hence the correct answer.