(1)感官动词或使役动词后的现在分词作补语表示动作正在进行，不定式作补语表示动作发生的全过程。
I saw him walking across the road.(正在穿过马路)
I saw him walk across the road. (看到过了马路的全过程)
(2)及物动词的过去分词(done)与现在分词的一般被动式(being done)都有被动意义，前者表示动作完成，后者表示动作正在进行。
The picture fixed on the wall was presented by a friend.(已经被钉在墙上了)
The picture being fixed on the wall was presented by a friend.(正被钉在墙上)
注意：不定式有表将来之意。
