问题补充：
Marymy letter;otherwise she would have replied before now.
A. has received
B. ought to have received
C. couldn’t have received
D. shouldn’t have received
答案：
A. has received
B. ought to have received
(答案→)C. couldn’t have received
D. shouldn’t have received
解析：注意单词otherwise引导虚拟语气。
