如果在关于x的线性回归方程y=a+bx中，b>0，那么对于x与两个变量间的相关系数r必有（）。
A.r>O
B.r<0
C.r=0
D.r=1
参考答案：A
The key to _____ the problem is to meet the demand _____ by the customers. [ ]
A. solving, making
B. solving, made
C. solve, making
D. solve, made
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