Because it starts with "although", you realize there is a negative point coming in the second part of the sentence, which leads us to C and D. However, D is the one which is correct, because, in fact the genetic variation is diminished by the process of cloning. The new living organism created is a copy of some other. This way, it has the same DNA. If it the were a traditional case of reproduction, the new living organism would have a different DNA code, which leads us to answer D.
