句子结构分析,求大神指点：It was 80 years before Christopher Columbus crossed the ...具体如下：It was 80 years before Christopher Columbus crossed the Atlantic ____ Zheng He had sailed to East Africa.A. when B. that C.after D.since答案为什么选B. D怎么就不对了?答案解析说是强调句型,可我把it was that去掉后,句子就是：80 years before Christopher Columbus crossed the Atlantic,Zheng He had sailed to East Africa.这句话说的通吗?我感觉是说不通.80 years before Christopher Columbus crossed the Atlantic作时间状语感觉怪怪的.如

句子结构分析,求大神指点：It was 80 years before Christopher Columbus crossed the ...具体如下：
It was 80 years before Christopher Columbus crossed the Atlantic ____ Zheng He had sailed to East Africa.
A. when B. that C.after D.since
答案为什么选B.
D怎么就不对了?
答案解析说是强调句型,可我把it was that去掉后,句子就是：
80 years before Christopher Columbus crossed the Atlantic,Zheng He had sailed to East Africa.
这句话说的通吗?我感觉是说不通.80 years before Christopher Columbus crossed the Atlantic作时间状语感觉怪怪的.如果是80 years ago,我还看得懂.
-----------------------
求大神指点!