Mary was much kinder to Jack than she was to the others of course made all the others

问题补充：

Mary was much kinder to Jack than she was to the others, , of course, made all the others upset.

A. who

B. that

C. what

D. which

答案：

A. who

B. that

C. what

(答案→)D. which

解析：考查非限制性定语从句。Which指代前面一句话的内容，在定语从句中做主语。句意：玛丽最Jack要比对别人更好，这一点当然让别人难过了。That不能引导非限制性定语从句；what不能引导定语从句。Who的先行词必须是人。故D正确。