By having to sleep in th open,he gets far closer to the world of nature than most of us ever do.
问题描述：
By having to sleep in th open,he gets far closer to the world of nature than most of us ever do.
这里的having起到什么作用?是动名词一般式吗?having to do是一个词组吗?这是新概念三27课的课文,译文：由于*在楼天睡觉,他比我们中许多人都离大自然近的多.谢谢!
答
have to do表示不得不怎样 表示她不得不在露天睡觉,就是议文中*的意思了,by是介词 后面要跟V-ing,所以用了having to do