Ponderous means to be very heavy in weight.
So a word most nearly opposite in meaning would be light.
Which means, having very little weight.
Another meaning of the word 'Ponderous' is to be very dull, boring, slow or awkward, Because of it's weight or and size.
So C would be wrong becasue it's not an opposite..
So the answer is A. You're correct. c:
Hope this helps. Have a nice day!!