【题目】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

【答案】B
【解析】句意：一想到回国就让他在国外工作时很开心。根据句意，用all作表语，而后面的kept him happy是修饰all的定语从句，修饰先行词all，关系代词只能用that，所以答案是B。