问题补充：
The farmer was very thankful to the doctor saved his son．
A. whom
B. which
C. who
D. whose
答案：
A. whom
B. which
(答案→)C. who
D. whose
解析：句意：那个农夫非常感激那个救了他儿子的医生。定语从句用来充当句中定语的成分，被修饰的名词叫先行词，连接主从句的是关系词。关系词分：1关系代词：who , whom , whose , which , that。2 关系副词：where,when why 等。一般的who 用于指代人的先行词，在从句中做主语或宾语（如果和介词连用指能用whom），whom也是指代人，在句中只能做宾语。分析句子结构，连接词在句中做主语，故选C.
