【题目】They went on well at first but eventually everything ________ they had worried about happened.
A.which
B.what
C.that
D.when

【答案】C
【解析】句意：他们开始进展得很好，但是最终他们担心的所有事情都发生了。先行词是不定代词everything，在定语从句中作宾语，不定代词作先行词，则关系词只能用that。故选C。