They arrived at a farmhouse ,in front of __sat a small boy. A.whom B.who C.which D.that 答

They arrived at a farmhouse ,in front of __sat a small boy.
A.whom B.who C.which D.that
答案是C我想知道为什么不能用AB,D我知道为什么不能用，因为of是介词所以不能用

C
本句考查定语从句，由于先行词为farmhouse【物体】，故不用who/whom【先行词为人士使用】
介词后不用that
in front of which指代in front of the farmhouse

选【c】属于介词+which引导定语从句的用法 farmhouse是物，所以不能用a和b； that不能放在介词之后，所以只能选c