It was when the private company successfully launched astronauts into space__________I knew

It was when the private company successfully launched astronauts into space__________I knew it would open up more opportunities in the space industry.
A. which B. how C. where D. that
【答案】D
【解析】
【详解】考查强调句型。句意：当私人公司成功地将宇航员送入太空时，我知道这将为航天工业开辟更多的机会。强调句型的结构为It is/was + 被强调部分+that/who +其它。当被强调内容为人时，用who,其它全部用that。该句式的特点为去掉It is/was和 that，其余部分在不添加内容的情况下，重写后依然为完整的句子。本句中去掉It is/was和 that，重写句子为：When the private company successfully launched astronauts into space, I knew it would open up more opportunities in the space industry.其中when…space,为时间状语从句，其余部分为主语。句子结构完整。所以，选项D符合题意。故选D。