The most likely explanation for the fact that the human genome consists of 3.2 billion bases,and encodes about 20,325 proteins,is that

A) all of the genome encodes protein.
B) the genome includes many copies of the instructions for each type of protein.
C) amino acids encode DNA sequences.
D) much of the genome does not encode protein.
E) each protein is encoded by about 160,000 DNA bases.