对两变量x和y同时进行简单相关分析和简单回归分析，其结果一定是（）
A.r＞0，b＜0
B.r＜0，b＞0
C.r＞0，b＞0
D.r＝b
E.r与b的符号无关
参考答案：C
解析：两变量x和y是正相关时，y随x增大而增大，回归系数b＞0；两变量x和y是负相关时，y随x增大而减小，回归系数b＜0根据r和b的公式和意义也可以看出，r和b的符号是相同的。
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| One day little Johnny went to visit his grandparents on their farm. He was given a slingshot (弹弓) to play with. He practiced in the woods, but he could 1 hit the target (靶子). 2 he got discouraged (气馁), he went back for lunch. As he was walking back, he saw Grandma's pet duck. 3 thinking, he took out the 4 , shot the duck in the head and 5 it. He knew Grandma loved that duck. She would be very 6 if she knew the truth, he thought. Then he hid the dead duck in the wood pile (堆), only to see his sister Sally 7 . She had seen it all, but she said 8 . After lunch Grandma said, "Sally, let's wash the dishes." But Sally said, "Grandma, Johnny told me he wanted to help in the 9 today, didn't you, Johnny?" And then she whispered to him, "Remember the duck?" So Johnny did the dishes. Later Grandpa asked 10 the children wanted to go fishing and Grandma said, "I'm sorry, but I need Sally to help me make supper." But Sally 11 and said, "Well, Johnny told me he wanted to help you." And then she whispered again, "Remember the duck?" So Sally went fishing and Johnny had to 12 at home. After several days of Johnny doing 13 his work and Sally's, he finally 14 stand (忍受) it any longer. He came to Grandma and said what he had done. Grandma said, "Johnny, I know. You see, I was standing at the window and I saw the whole thing. But because I love you, I 15 you. I was just wondering how long you would let Sally make a slave (奴隶) of you." | ||||
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