Which of the Following Contradicts the One-Gene,one-Enzyme Hypothesis

Which of the following contradicts the one-gene,one-enzyme hypothesis?

A) A mutation in a single gene can result in a defective protein.
B) Alkaptonuria results when individuals lack a single enzyme involved in the catalysis of homogentisic acid.
C) Sickle-cell anemia results in defective hemoglobin.
D) A single antibody gene can code for different related proteins, depending on the splicing that takes place post-transcriptionally.
E) Two enzymes are able to metabolize the same reaction.