Why is it that rna can catalyze reactions but dna cannot?

The choices for this question can be found elsewhere and as follows:

A.The sugar of RNA is much more reactive than the sugar of DNA. 
B.The bases of RNA are much more reactive than the bases of DNA. 
C.The phosphate groups of RNA are much more reactive than the phosphate groups of DNA. 
D.The primary structure of RNA is fundamentally different than the primary structure of DNA.

The correct answer is option A. RNA can catalyze reactions because the sugar of RNA is much more reactive than the sugar of DNA. The extra OH on the 2' carbon makes the difference. 

Apparently the correct answer is carbohydrates