watch +do（不+to ）是 “看见某人做过某事”已经做过了、
watch doing 是“看见某人正做某事”是正在做、
I often watch him read books in his bedroom.
我经常看见他在房间里读书、（这件事做完了）
I watch him reading books when I go to his bedroom.
当我走进她的房间时,他正在读书、 （正在做）