现在分词作定语的例句请比较一下,然后告诉我这两句话(作定语的现在分词短语在意义上相当于一个定语从句）的不同之处及原理是什么.The man standing by the door is my English teacher.The man who is standing by the door is my English teacher.Did you see the homeless man sleeping under the bridge?Did you see the homeless man who was sleeping under the bridge?

Did you see the homeless man sleeping under the bridge?
这句话可以理解为, 这个人正睡在桥下, 睡在桥下这个动作是在看的同时发生的.
Did you see the homeless man who was sleeping under the bridge?
而这句话,定语从句用的是was 过去时, 说明那个人曾经睡在桥下,而现在没有.
The man standing by the door is my English teacher.
The man who is standing by the door is my English teacher.
这2句我认为没有区别, 都表示正站在门边的男人是我的英语老师.

有没有who is其实没有什么大不同 可加可不加

The man standing by the door is my English teacher.
standing作为形容词修饰这个男人,限制翻译,只可以译为,站着的男人.
The man who is standing by the door is my English teacher.
who作为引导词引导定从,[某个男人,站着的男人]你就这么理解吧.
以上两句意思是一样的.也么撒区别,看个人喜好爱用哪个用哪个.
下两句同理

Thefallingleaveslookbeautiful.正在下落的树叶看起来很漂亮。