问题补充：
She your birthday party, but she had to look after her mother in hospital．
A. should attend
B. ought to have attended
C. can have attended
D. must have attended
答案：
A. should attend
(答案→)B. ought to have attended
C. can have attended
D. must have attended
解析：考查情态动词用法。本题是虚拟语气，根据but后面的had说明本题是对过去情况的虚拟，使用情态动词+have done的形式。C项表示推测，指可能做了某事；D项指一定做了某事；ought to have done本应该做某事，实际上却未做；句意：她本应该来参加你的生日聚会的，但是她不得不照顾她生病住院的妈妈。故B正确。
