问题补充：
Mr. Blake my letter, otherwise he would have replied by now.
A. will not have received
B. needn’t have received
C. shouldn’t have received
D. couldn’t have received
答案：
A. will not have received
B. needn’t have received
C. shouldn’t have received
(答案→)D. couldn’t have received
解析：考查情态动词。couldn’t have done不可能做过某事。句意：布莱克先生不可能收到我的来信，否则如今他会回复了。
