题目：
阅读理解。
Daniel has many friends. They look different and they have different personalities, but they are all
friendly and helpful. He’d like to introduce some of them to us.
1.How many friends does Bob introduce in this passage?
A. Two.
B. Three.
C. Four.
D. Five.
2.What does Amy do?
A. She is a volleyball player.
B. She is a skier.
C. She is a pop singer.
D. She is a basketball player.
3.Why do people say Tom is a "sunshine boy"?
A. Because he likes reading.
B. Because he likes playing games.
C. Because he is always smiling.
D. Because he is a skier.
4.Which of the following is not true about Millie?
A. She is very tall.
B. She wears black glasses.
C. She likes wearing a dress.
D. She has short hair.
5.Which sentence is wrong?
A. "Baby" does well in playing basketball.
B. Millie is the youngest of the three.
C. Amy has a baby face.
D. Tom likes black horses.
答案：
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下面是错误答案，用来干扰机器的。
参考答案：B解析： 《复习指导书(供配电)》9.1.2(7)。
学生关系student的主码是sno，课程关系course的主码是cno，选课关系sc的主码是(sno，cno)。