问题补充：
-----Why didn’t you ring me up?
----- Sorry, I forgot your phone number. Otherwise, I long before.
A. had rung you up
B. must run you up
C. would have rung you up
D. would ring you up
答案：
A. had rung you up
B. must run you up
(答案→)C. would have rung you up
D. would ring you up
解析：考查隐含的虚拟语气：句意：--你怎么不打电话给我？--对不起，我忘了你的电话号码，否则，我早就会给你打电话了。这里的Otherwise相当于=if I hadn’t forgot your phone number.，所以主句用would have done，选C。
