Is this the reason _______ he was late for the meeting?
A．why
B．when
C．where
D．what
答案：A
试题分析：考查定语从句。先把原句改为陈述句：This is the reason________ he was late for the meeting.，可以看出，先行词是the reason，定语从句“he was late for the meeting”是主系表结构，不缺少成分，用关系副词why引导，what不用于定语从句，故选A。 考点：考查定语从句