For more than five decades, the IMF has been implementing it

This particular topic is about tense agreement which means all parts that make up the statement must agree with one another.

Option A:- Incorrect
This isn't consistent with reality that even though it started decades ago, the implementation is still continuous and must be in present continuous tense.

Option B:- Incorrect
The keyword here is "implementing" which takes the shape of present continuous tense. Therefore, a consolidating word that appear next must be in the present continuous tense too in this case "demanding".

Option D:- correct
This is a case of misinterpreted object statement i.e the whole statement in place of subject statement has taken an object dimension and therefore has a different meaning.

Option E:- Incorrect
This is not consistent with the forward thinking present continuous tense as explained in the previous option.