20.it was twenty years ago ______ he joined the party.
问题描述：
20.it was twenty years ago ______ he joined the party.
A)as
B)when
C)since
D)that
答
It is...that...It was ...that...
是强调句型的固定用法.
强调句型
i．强调谓语或者其他成分
1．强调谓语动词一般在谓语动词原型前加do／does／did.时态是一般现在时,在动词原型前加do／does,时态是一般过去时,在谓语动词原型前加did.
2．强调句子其他成分用强调句型：“It+be+被强调成分+关系代词who／that+句子的其他成分”.
注意：
1)被强调的成分是人时,关系代词可以用who／that,强调其他成分时(除谓语动词外)一律用that.
2)在强调句中'be动词通常只有两种形式：一般现在时is,一般过去时was,但是不能排除带有情态动词的形式.