He is the only person who saw the accident ______ (happen). so he is the most important witness.
问题描述：
He is the only person who saw the accident ______ (happen). so he is the most important witness.
空里为什么填 happen 啊?
答
happen是发生的意思
所以整个句子的意思是 “他是唯一一个看见事故发生的人,所以他是最重要的目击证人”
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