Helen was much kinder to her youngest son than to the others of course made the others

问题补充：

Helen was much kinder to her youngest son than to the others, , of course, made the others envy him.

A. who

B. which

C. what

D. that

答案：

A. who

(答案→)B. which

C. what

D. that

解析：句意：海伦对她的最小的儿子比对其他的孩子要好得多，这使其他的人很是嫉妒。that和 what不能引导非限制性定语从句；这是非限制性定语从句，先行词是前面的句子，故排除A，故选B。