问题补充：
The number of people invited fifty, but a number of them absent fordifferent reasons．
A. were; was
B. was; was
C. was; were
D. were; were.
答案：
A. were; was
B. was; was
(答案→)C. was; were
D. were; were.
解析：本题考查主谓一致。a number of + 复数名词/代词，在句中作主语时，谓语动词用复数，而the number of + 复数名词/代词，在句中作主语时，谓语动词用单数，
