was known to them that the boss had broken his promise he would give them a rise.A. What;

问题补充：

was known to them that the boss had broken his promise he would give them a rise.

A. What; what

B. It; which

C. It; that

D. As; that

答案：

A. What; what

B. It; which

(答案→)C. It; that

D. As; that

解析：这里that引导的主语从句是句子的真正主语，所以需要It作形式主语；在主语从句中，又包含一个同位语从句，引导词在同位语从句中不作任何成分，且无实际意义，故用that引导。