【题目】—Jack had no confidence and courage at that time.
—That was the reason ________ he gave up the plan. （ ）
A.why
B.when
C.what
D.how

【答案】A
【解析】A．why在定语从句充当原因状语；B．when定语从句中做时间状语；C．what定语从句无此关系词；D．how定语从句无此关系词；句意：—那是杰克没有自信心和勇气。—这就是他放弃计划的原因。根据句意，故选A.