watch,see,hear sb do sth 表示看着,看见,听见某人做过某事,强调事情已经做过
watch,see,hear sb doing sth 表示看着,看见,听见某人正在做某事,强调正在做
find,sb doing sth 发现某事正在做某事
I watched (saw) him play basketball.我看见他打篮球了.
I watched (saw) him playing basketball.我看见他正在打篮球.
I heard him sing an English song.我听见他唱英文歌了.
I heard him singing an English song.我听见他正在唱英文歌.