问题
单项选择题
Mary couldn’t have received my letter; otherwise she______before now.
A．would have replied
B．has replied
C．must have replied
D．had replied
答案
参考答案：A
解析： 16．此名为假设条件被隐蔽的虚拟句，可还原为If Mary had received my letter, she would have replied before now。