What Accounts for the Differences Between the Number of Protein

What accounts for the differences between the number of protein coding genes in the genome and the number of different proteins expressed?

A) Not all genes are translated,so the number of expressed proteins is lower than the number of protein coding genes.
B) Not all genes are transcribed,so the number of expressed proteins is lower than the number of protein coding genes.
C) Alternative splicing is very common and increases the diversity of expressed proteins so the number of expressed proteins is higher than the number of protein coding genes.
D) Alternative splicing is very common and decreases the diversity of expressed proteins so the number of expressed proteins is lower than the number of protein coding genes.
E) Protein turnover is rapid and decreases the diversity of expressed proteins so the number of expressed proteins is lower than the number of protein coding genes.