Which of the Following Statements Supports the One Gene-One Enzyme

Which of the following statements supports 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 multiple enzymes involved in the catalysis of homogentisic acid.
C) Sickle-cell anaemia results in normal haemoglobin.
D) Multiple antibody genes can code for different related proteins, depending on the splicing that takes place post-transcriptionally.