DNA and RNA are polymers of nucleotides which are made up of sugar, nitrogenous base and phosphate moiety. Phosphate group is common to both DNA and RNA which makes options B and D wrong. There are two types of nitrogenous bases; purines and pyrimidines. Purines are namely adenine and guanine and three pyrimidines are cytosine, thymine and uracil. The purines adenine and guanine and the pyrimidine cytosine are common to both DNA and RNA. DNA has the pyrimidine thymine; RNA has the pyrimidine uracil. The deoxyribonucleotide units of DNA contain 2 deoxy-D-ribose sugar, and the ribonucleotide units of RNA contain D-ribose sugar; the difference lying in absence of an oxygen atom at 2’ position, not in number of carbon atoms. This makes option C wrong. Thus, DNA and RNA differ in nitrogenous bases and sugar. Option A is correct.