谁来给我解释一下这两个英语句子的语法?

题目

谁来给我解释一下这两个英语句子的语法?
1.If Greg had tried harder to reach the opposite shore, we （would not have had ）to pick him up in the boat.
2. The lecture （having begun）,he left his seat so quietly that no one complained that his leaving disturbed the speaker.
关键是括号里面的东西不太懂.谢谢!

答案

1.虚拟语气,这句话表达的是与过去事实相反的虚拟语气.结构是 if --- had done---,----- would have/have not done sth
2.独立主格结构,begin 的主语是lecture,而不是主句中的主语he.也就是说从句有自己的主语.但是一个句子中只能有一个谓语动词,为了避免两个动词的错误.所以have begun 变成 having begun.因为是主动态 所以用ing形式