The human genome contains approximately 20,000 protein-coding genes, yet it has the capacity to ...

The human genome contains approximately 20,000 protein-coding genes, yet it has the capacity to produce several hundred thousand gene products. What can account for the vast difference in gene number and product number?
 
  A) Much of the DNA is in the form of trinucleotide repeats, thus allowing multiple start sites for different genes.
  B) There are more exons than introns.
  C) Alternative splicing occurs.
  D) There are more introns than exons.
  E) Every gene can be read in both directions, and each gene can have inversions and translocations.