Explanation:

Correct Answer is (a).The original sentence is erroneous.
Reason: The word ‘affect’ means ‘have an effect on’ which is unsuitable in this sentence. The correct word to be used here is ‘effect’ which means ‘cause (something) to happen’.
Moreover, the word ‘meaningful’, which means ‘serious, important, or worthwhile’, should be used in place of ‘mean’ so as to make the sentence contextually correct.
Among the given choices, only option A replaces the given bold part most appropriately.
The sentence after replacement becomes:
The terms of bank chairpersons must be elongated in order to effect meaningful changes and to hold them accountable.Option A is hence the correct answer.