问题补充：
Having been ill in bed for about two months,he had a hard time toclimb the hill我想知道开头为什么用having been?其他形式的非谓语为什么不可以?
答案：
Having been ill in bed for about two months,he had a hard time toclimb the hill
这里的Having been ill in bed for about two months是一个【现在分词短语】,在句中作【原因状语】,相当于一个【原因状语从句】.
Having been ill in bed for about two months,he had a hard time toclimb the hill=Because he had been ill in bed for about two months,he had a hard time toclimb the hill.
======以下答案可供参考======
供参考答案1:
开头用having been是表示伴随状态的，而且是主动的，只能用现在分词
我是自己写的哦，请采纳O(∩_∩)O谢谢
供参考答案2:
表主动,表完成对现在造成的影响,而且是自然而然的影响
