(A-hui comes home from work and sees his mother standing at the door.)

A-hui: Hey, Mom. You look worried. Anything wrong?

Mrs. Liu: Your sister hasn't come back yet. She never comes home later than five-thirty.

A-hui: It's ten to six now. Did you call the school?

Mrs. Liu: I did. They said Mei-ling left at four-thirty.

A-hui: How about her classmates? We should call them.

Mrs. Liu: I've called five of them, and they all have no idea where she is.

A-hui: Let me get my bicycle. I'll ride around and look for her.

Mrs. Liu: Aren't you going to have dinner with your girlfriend tonight? You might be late.

A-hui: Don't worry, Mom. I'll call her later. It's more important to find Mei-ling. Why don't you go inside and wait? Mei-ling might call home at any time.

Mrs. Liu: You're right, and I should call more of her classmates. Ride carefully, OK?

A-hui: I will, Mom.

What is Mrs. Liu worried about?
Her daughter is not doing well at school.
Her son has not been able to find a job.
Her son is riding his bicycle.
Her daughter has not come home.
What has Mrs. Liu done about her problem?
She talked to her friends.
She made several phone calls.
She tried to get more sleep.
She went biking.
Who is her?
Mei-ling's classmate.
Mrs. Liu.
A-hui's girlfriend.