Explanation:

The original sentence is erroneous.

Reason: Usage of the phrasal verb 'put down' which means ‘suppress' is inappropriate in this sentence.

'Put by' which means ‘lay aside for time of need’ would be suitable in this context.

E.g.: I try to put by some money every month.

Hence ‘put aside’ should be used in place of ‘put down’ to make the sentence grammatically and contextually correct.

Among the given choices, only option B replaces the given bold part most appropriately.

The sentence after replacement becomes:

Entrepreneurs should put by some money in a contingency fund even before starting their business.

Option B is hence the correct answer.