Jimmy was five years old and his brother, Billy, was only a baby. One morning his mother waited for an important telephone call for hours, but nobody called. There was no bread in the house and she had to go out to buy some. Jimmy stayed at home to look after the baby. When the mother was out, the telephone rang and Jimmy answered.
Mr. Baker: Hello! May I speak to Mrs. White?
Jimmy: Sorry, Mother is out.
Mr. Baker: Well, when she comes back, say to her, 〝Mr. Baker called."
Jimmy: What?
Mr. Baker: Mr. Baker. Write it down. B-A-K-E-R.
Jimmy: How do you write B?
Mr. Baker: How do I write...? Listen, little boy, is there anybody else with you? Any brothers or sisters?
Jimmy: Yes, my brother Billy is here.
Mr. Baker: Good. I want to talk to him, please.
Jimmy: All right. Jimmy took the telephone to the baby's bed and put it beside its head. Not long after that his mother came back.
Mother: Did anybody call?
Jimmy: Yes, a man called. But he only wanted to talk to Billy.
Jimmy's mother went out because ____.（ ）
参考文章第三句。
