Is this the reason _______ at the meeting for his carelessness in his work?(2002上海春招)

问题描述:

Is this the reason _______ at the meeting for his carelessness in his work?(2002上海春招)
A.he explained B.what he explained C.how he explained D.why he

选A 定语从句,省略关系词which that 在定语从句中做宾语
忘得分.