Answer:
D.
Explanation:
A conditional mood is a request or in condition of something happening in the future; it uses auxiliary verbs.
It is not A because it is a demand and a statement.
It is not B becaus it is a demand.
It is not C because C is in condition of something that has already happened in the past.
It is D because it is a request.
This suggests a possibilty, whether it is through a request (requests can be denied or accepted) or scenario in which things are suggested to alter the future, even if it can't be changed.
