Question

【题目】_______ caused the accident has not been found out yet.

A.WhatB.Which

C.The thingD.That

Answer 1

【答案】A

【解析】

考查主语从句。句意：造成事故的原因还没有查明。此处为主语从句，从句中缺少主语，应该用what引导，故A项正确。