很简单,就是把主格给隔离出来
记住句型：
主语（A）(这个就是独立主格)+分词（to do,doing ,done,介词短语,形容词等）,主语（真正）+谓语+其它成分
逗号前后的位置可以变化：
如：He hearing the bad news,his face turned pale.
意思：他一听到那个坏消息,他的脸就变的苍白.
He指主语（A）,His face是真正主语,必须是两个主语.
1.______ no bus,we had to walk home.
A.There was B.There being C.Because there being D.There were
选B,主格there+分词being
2.____,I'll go there with you tomorrow afternoon.
A.Time permits B.If time permitting C.Time permitting D.Time's permitting
选C Time是独立主格+分词permitting
其上的例子都是主动的用的是doing,但有done等其他的都可以,