问题补充：
The number of people invited fifty, but a number of them absent for different 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：the number of修饰可数名词复数形式，谓语动词用单数形式；a number of修饰可数名词复数形式，谓语动词用复数形式，故本题C项正确。
