How many types of nucleotides are in dna and how do they differ?

There are four: adenine, thymine, guanine, and cytosine.
cytosine and thymine both are short bases also called pyrimidine
adenine and thymine are long bases also called purine
adenine bonds with thymine and both have equal proportions
cytosine bonds with guanine and both have equal proportions

I’m not really sure

The answer is c) tons