When the Human Genome Was Sequenced, We Learned That There

When the human genome was sequenced, we learned that there are fewer than expected protein coding genes (approximately 20,000) . Yet, the total number of proteins produced in humans approaches 100,000. What accounts for this discrepancy in numbers?

A) We have not yet identified all of the open reading frames in the human genome.
B) We have not yet fully sequenced the human genome.
C) mRNA processing mechanisms allowmultiple proteins to be produced from a single DNA sequence.
D) Some noncoding DNA sequences encode proteins.
E) There has been a gross over-estimation of the number of proteins produced in humans.