is surprising to us is that Tom for English was once boring can speak English fluently

问题补充：

is surprising to us is that Tom, for English was once boring, can speak English fluently as though he were a native speaker.

A. What; whom

B. What; whose

C. It; whose

D. As; whom

答案：

(答案→)A. What; whom

B. What; whose

C. It; whose

D. As; whom

解析：考查主语从句的定语从句。本题第一空是what引导的主语从句what is surprising to us,what在句中做主语。第二空是一个定语从句，whom指代Tom作为介词for的宾语。句意：让我们惊讶的是Tom能够讲流利的英语就好像是他的母语一样。，对他来说英语曾经很乏味。故A正确。