Which of the Following Is Incorrect

Which of the following is incorrect?

A) The deferral of realized gain on a § 1031 like-kind exchange is mandatory.
B) The deferral of realized gain on an indirect (into cash and then into qualified property) § 1033 involuntary conversion is mandatory.
C) The taxpayer can elect to forgo the exclusion of realized gain on a § 121 sale of residence.
D) Both b. and c. are incorrect.
E) a., b., and c. are incorrect.