A and D should be the answer.
ans is A but why you choose A .It's bit confusing in ring
can you explain me?
Look! In first fig on the upper Pentagon, both CH3 is above the plane. For checking distereomers you just put a mirror between both fig, now u can clearly see that in the 2nd fig, on the upper Pentagon, one Ch3 is above the plane, and another is below. So both can't be mirror image of each other.
Also , D will not be the ans as both are same compound.