谁能给我解释一下感官动词后边什么时候用do什么时候用doing

谁能给我解释一下感官动词后边什么时候用do什么时候用doing
有人说看到正在进行用doing,经常性的过去的用do
看几个例题,完全混了.
A woman saw it happening when she was walking past.
I heard lily singing in the next room right now.
Mary saw Tom playing football in the street,so she told hin not to
play in the street.
i often hear her sing this song and heard her singing it when you phoned me a moment ago.
i always see lily reading books at home.