surprised me most was　such a little boy of seven

surprised me most was　such a little boy of seven could play the violin so well. What.
A; that
C. That; what B. What. That; which D

be

答案b 考查名词性从句。what引导主语从句what surprised me most，并在句中做主语。that引导表语从句that such a little boy of seven could play the violin so well.因为这个表语从句很完整，所以使用that引导，that没有任何意思，只起连接作用。