It was after he got what he had desired_______he realized it was

It was after he got what he had desired_______he realized it was not so important.
A、that
B、when
C、since
D、as
【正确答案】：A
【题目解析】：考察强调句：这是一个强调句,句型为：It is (was)+被强调部分(主语、宾语或状语)+that(who)..