Which of the following correctly explains the relationship between xanthine dehydrogenase (XDH)and xanthine oxidase (XO)?

A)in healthy tissue,XDH is abundant while XO is rarely found
B)conversion of XDH to XO occurs under conditions that damage cells
C)XDH is converted to XO by formation of a disulfide bond
D)XDH is converted to XO by proteolysis
E)all of the above