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
B. all that
C. all what
D. Which
解析：
主要测试表语从句。在平时的学习中应该注意总结，在引导名词性从句时引导词
what等同于all that，即相应的转化为了定语从句。例如：What you said is right。（主语从句）= All that you said is right。（定语从句）你说的是对的。另外题干中 kept him happy 正好缺少主语。所以可以用what来引导表语从句同时充当句子的主语，进而结合上面所述what = all that。所以答案为all that 最佳。句子意思：当他在国外工作的时候，回国的想法一直让他非常高兴。