The thought of going back home was kept him happy while he was working abroad.
A. that
B. all that
C. all what
D. which
网友回答
A. that
(答案→)B. all that
C. all what
D. which
解析：句意：回家的想法是他在国外工作的时候所有的让他高兴的事情。这里用all表示“所有的事情”，后面是定语从句，因为在定语从句中做主语，所以关系代词不能省略，而且先行词是不定代词的时候，定语从句用that引导，所以选B。