设随机变量X，Y独立同分布，且X的分布函数F(X)，则Z＝max｛X，Y｝的分布函数为()．
A. F2(X)
B. F(x)F(y)
C. 1－[1－F(x)]2
D. [1－F(x)][1－F(y)]
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设A是m×n阶矩阵，下列命题正确的是()．
A. 若方程组AX=0只有零解，则方程组AX＝b有唯一解
B. 若方程组AX=0有非零解，则方程组AX＝b有无穷多个解
C. 若方程组AX＝b无解，则方程组Ax＝0一定有非零解
D. 若方程组AX＝b有无穷多个解，则方程组AX＝0一定有非零解
How many circles contain a black dot？
A. 12.
B. 13
C. 14
D. 15
Lead time is an important concept of a person's culture that is ______.
A. learned casually and without planning
B. vague because its rules have not been stated technically
C. not taught formally in the classroom
D. only learned through experience
According to the passage, consumerist culture ______.
A. cannot thrive on a fragile economy
B. will not aggravate environmental problems
C. cannot satisfy human spiritual need
D. will not alleviate poverty in wealthy countries
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