has finished the work ahead of time will be rewarded though we dont know who it will be.

问题补充：

has finished the work ahead of time will be rewarded though we don know who it will be.A．Those whoB．AnyoneC．WhoeverD．No matter whoC

答案：

(答案→)C

解析：首先判断will be rewarded是谓语，前面应当是主语。如Those 是主语，who引导定语从句。如Anyone是主语，又多少了一个引导定语从句的关系代词who。所以选项D只能引导状语从句。