Which of the Following Statements Is LEAST-Likely True

Which of the following statements is LEAST-Likely true?

A) Exhaust systems can rust out because there are acids and a good deal of moisture in the engine's exhaust.
B) An engine that is never fully warmed up will experience rapid rusting in the exhaust system because the moisture never gets a chance to dry out.
C) Mufflers often rust out on the highest end.
D) Usually the first clue that there is a leak in the exhaust system is the sound of leaking exhaust.