Question

PLEASE EXPLAIN TO ME!!? which is an answer?!

Answer 1

They all can be answers 

Answer 2

The answer is D because it is the only way for there to be a congruent (Exactly the same) image with the exact same vertices (the points of the parallelogram).  If you picture cutting this shape out of a piece of paper and turning 180 degrees counterclockwise, you'll find it will be in the exact same position