when i was at your age my father told me that i should go and work whereve___most.

这里是状语从句的省略。状语从句里有主语和be动词，可以一起省掉，所以这里写完整就是wherever I was needed.

如果你选A，就把wherever当做主语了，这个成分是关系副词，只能做状语，不能做名词性成分的主语。