题目内容：

The school bell rang loudly. Everybody packed their bags and got ready to go home. Usually David's mother would take him home from school but today she was not there. David waited for 15 minutes before he walked home.

When he reached home, he knocked on the door as he did not bring his keys. To his surprise, no one answered the door. David thought his mother was in the toilet so he waited patiently for her. After a few minutes there was still no answer.

David knocked again but still no one answered. He was about to go to the nearby coffee shop where his father worked to get the keys, when he heard the friendly voice of his neighbor, John.

David told him that no one was at home and John's mother suggested that David stay in their house to wait for his mother. David and John played happily till evening when David's mother came back.

David thanked John and his family before he went back to his house. David's mother explained to David that she had a backache and she had to see the doctor. From this experience, David learnt an important lesson, "Neighbors are people who help each other."

根据短文内容，回答下列问题。

1.How long did David wait before he went back home on foot?

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2.Where did David's father work?

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3.When did David's mother come back home that day?

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4.Where might David's mother be when he reached home?

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5.What was wrong with David's mother?

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