现在分词构成复合结构
1.不少动词可用现在分词构成复合宾语：
I saw Tom waving to me.我看见汤姆向我挥手。
He heard someone knocking at the door.他听见有人敲门。
I am sorry to keep you waiting.对不起让你久等了。
We found a tree lying across the road.我们发现一棵树拦在马路中间。
这些都可作为句型来记，如hear somebody doing something, see somebody doing something，还有keep, notice, find, leave等动词可跟这样的宾语。
2.在see, hear, notice这类动词后，有时可跟两种复合结构，一种由现在分词构成，一种由不带to的
不定式构成：
We saw a man standing there.我们看见一个男子站在那里。
We saw a man leave the house.我们看见一个男子离开了那座房子。
前者表示动作正在进行，后者表示动作业已完成，有时两种结构差别不大，可以换用，如：
I often heard her singing this song.我常听见她唱这首歌。
sing
3.这种结构也可用于被动形式：
He was often seen working in the fields.人们常常看见他在地里干活。
She was once heard singing this song.有一次人们听见她唱这支歌。
4.介词后间或也跟这种复合宾语：
She listened to him playing the piano.她听他弹钢琴。
He looked at the children playing under the tree.他看孩子们在树下玩耍。