第1个回答 2012-10-10
动词-ing有两种意义。
一种是：动作在某时刻正在进行，称为动词的现在分词。
还有一种是：动词在做非谓语的成分时，不能用原形，有时要用ing形式，称为动名词。有时也用to do 即动词不定式。
一、动词-ing形式做主语
1、现在分词做主语表示事物化、抽象化的概念。强调：现在分词做主语时谓语一律用单数。
Eg: Talking is an art.
Eg: Tearning English well is not easy.
2、it做形式主语的情况
It’s no good/use doing sth. 做``````是没有用的
It’s useful/useless doing 做``````是有/没有用的
There is no `````````doing sth.
Eg: It is no use crying after knowing the result.
Eg: It is no good playing games.
二、动词-ing形式做表语
动词-ing形式做表语，一般表示比较抽象的习惯性动作。
1、句子主语常是表示无生命的事物的名词/抽象的习惯性动作。（主语和表语的位置可以互换）
Eg: My hobby is playing games.--------Playing games is my hobby.
Eg: One of his bad habits is speaking loudly. -----------Speaking loudly is one of his bad habits.
Eg: Your task is studying hard.-------------Studying hard is your task.
与现在进行时的区别：
He is flying.(现在进行时，就不能转换成----------Flying is he)
2、表示主语的某种性质或状态，描述主语的特征，相当于形容词，故不能与主语互换。
系动词：be动词、感官动词、get/become等。
Eg: This film is interesting.
Eg: Today’s weather is nice.
Eg: The song sounds good.
(主语一般为物：moving\ surprising\promising有希望的)
三、动词-ing形式做宾语
1、作动词的宾语
某些动词后只能用动词-ing形式作宾语，不能用不定式。
allow \ cannot help\ consider\ risk\ suggest\ forbid\ protect```(from)阻止\ admit\ advise\ allow\ avoid\ delay推迟\ enjoy\ escape逃脱\ finish\ give up\ imagine\ mind\ practise\
Eg: I tried to avoid making mistakes.
Eg: I suggest having a rest.
2、作介词的宾语
是一些固定的短语搭配：be/ get/ become used to习惯于, look forward to, insist on, be succed in, be fond of, be interested in, be worth, devote```to, stick to, lead to and so on.
Eg: The book is worth reading.
Eg: I am used to getting up early.
四、作宾语补足语
1、动词-ing形式可以在感官和心理状态的动词后面作宾语补足语，和宾语一起构成复合宾语。（表示动作的正在进行，状态正在持续）
Eg: I watched a student picking peaches when I crossed the school.
Eg: When I came into classroom, I heard someone singing.
3、动词-ing形式也可以用在使役动词have\ get\ leave\ keep\set\ send等动词后作宾语补足语。
（宾语与作宾补的现在分词之间存在逻辑上的主谓关系，即宾语是现在分词动作的发出者。）
Eg: Don’t have your students doing homework all the time.
五、动词-ing形式做定语
1、表示被修饰词的某种用途,一般放在所修饰词的前面。
阅览室 reading room 吸烟室 smoking room
洗衣机 washing machine 写字台 writing desk
3、起形容词作用的动词-ing作定语时，含有主动和进行的意思。
(1) 单个的分词放在所修饰名词的前面
Eg: I walked quietly in order not to wake the sleeping bird.
(2) 短语放在所修饰的名词后面
Eg: I know the bird sleeping in the tree.---------I know the bird which is sleeping in the tree.
Eg: It lived in a tree facing my house.----------It lived in a tree which faced my house
第4个回答 2012-07-12
主要有以下几种情况
1 某些固定搭配中。如practise doing
2 用作伴随状语。如Hearing the news,I feel so good.
3 充当主语时。如 running is good for your health
4 用于with构成的一些结构中。如 with the bell ringring，the students all stand up
现在想起的就这些 楼主可以翻翻语法书