[请教] GMAT&LAST Test A Q7

If A, then B.

If B, then C.

If C, then D.

If all of the statements above are true, which of the following must also be true?

(A) If D, then A.

(B) If not B, then not C.

(C) If not D, then not A.

(D) If D, then E.

(E) If not A, then not D.

Answer is C, why?

逆否命题成立.

现在这类题GMAT已经不考了.楼主可以不必看这类题.

用集合来做，画几个圈,如果没学过看看概率第一章