She is a cute, quiet girl. As a daughter, she has no secrets from her mother, who is very pleased with
her. But these days she has become not so open as before. She has a diary that she keeps under lock and
key (严密保管). Her mother cannot help worrying about her: what if she falls in love, which is too early
of her age? After all she is reaching the "dangerous time". These thoughts have caused trouble in the
mother's mind.
     One weekend the girl came to tell her mother that she was going to the cinema with her schoolmate
and would return late. This was the first time her mother agreed, and she couldn't help worrying because
her daughter had never been away at night before. The mother waited till nine. She decided to go out to
meet her daughter. Just at that time the noise of a car drew her to the window and---there was her
daughter, waving goodbye to a boy. Her heart missed a beat. When the girl came in, the mother was
watching TV, just like nothing had happened. "Mum, I'm back." "Yeah." "Sorry to be late. Still sitting up?"
 "Yes. Oh, that… Who's that boy?" The daughter was stunned (发楞) for some time. "Ah. It's my monitor.
He gave me a lift on his way home. Mum, I'm going to bed." "All right. Go to sleep early."
     Next morning when the mother went to the daughter's room to do some cleaning, she found her diary
left on the bed. After a few minutes'thinking, she at last opened it to the page of the night before. It reads:
Mum, it's love that made you ask, but it would show your understanding of me if you hadn't.
can't help doing sth: 禁不住做某事