A good conclusion should be based on

A.

guesses

B.

beliefs

C.

opinions

D.

facts

The answer would be D. It is important to really sell the idea in the final the paragraph, without of course giving too much new information, but more of a restatement of your other given reasons. Also, the other answers are all really similar just synonymous, so if one of them is right, then all of them would also have to technically also be right.