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. 

Increase in atmospheric oxygen by the photosynthetic organism to the biosphere evolved more complex forms of life. Many different plants, animals consuming plants, bacteria decomposing dead plants and animals evolved.These forms a food web in the biosphere. The remains of dead plants and animals release nutrients to the soil and ocean which are reabsorbed by the other growing plants.This food exchange  and energy exchange make the biosphere a self supporting and self regulating system .