The correct answer is A.
Oswald Avery applied several biochemical techniques to large cultures of bacteria in order to extract and purify the "transforming principle". Their experiments showed that most probably the "transforming principle" was DNA. One of the observations leading to this conclusion was that enzymes that degrade proteins or RNA (such ribonucleases) had no effect on the "transforming principle". On the contrary, enzymes degrading the DNA destroyed the extract's transforming capacity.
