什么时候应用动词原形？动词不定式？动名词做主语？

祈使句中用动词原形做主语
例如Open the door, please.
一般用动名词，或不定式都行
例如：Watching movies is interesting
To watch movies is interesting

动词原形打头时，一般都是祈使句，例 Open the window please,
动词不定式打头时，一般带有命令性和目的性。 To remember his telephone number, I can't
go to sleep for a night.
动名词做主语的用法
动名词做主语往往表示经常性,习惯性的动作, 在口语中也可以表示具体的动作.如:
Seeing is believing.
Helping her is my duty.
动名词
Talking mends no holes.
空谈无济于事.
Working with you is a pleasure.
和你一起工作是一种乐趣.
动名词做主语和不定式做主语一样,也可以用it作形式主语.如:
It's rather tiring walking around in a city.
不定式做主语往往表示具体的特别是将来的动作.如:
It's no use crying over spilt milk.
覆水难收.
过去分词做句首状语，它与现在分词、不定式的区别如下：
现在分词与过去分词作状语的区别。
现在分词做状语与过去分词做状语的最主要区别在于两者与所修饰的主语的主动与被动关系的区别。
1）现在分词作状语时，现在分词的动作就是句子主语的动作，它们之间的关系是主动关系。
He went out shutting the door behind him.
他出去后将门随手关上。
Not knowing what to do, he went to his parents for help.
由于不