The number of people invited fifty but a number of them absent for different reasons. A

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。