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问题 选择题

两串联电解池，左边放硫酸铜，右边放一定量的某硝酸盐溶液，电解时当左池有1．6gCu析出时，右池析出0．45g固体，则右池溶质为[ ]

A．AgNO3

B．NaNO3

C．Mg(NO3)2

D．Al(NO3)3

答案

答案：A

单项选择题

______是线性结构的数据结构。

A．列表

B．高维数组

C．双端队列

D．二叉树
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单项选择题

Low-income families are often unable to afford as much child care as they need. One government program would award low-income femilies a refund on the income taxes they pay of as much as $1,000 for each child under age four. This program would make it possible for all low-income families with children under age four to obtain more child care than they otherwise would have been able to afford.
Which of the following, if true, most seriously calls into question the claim that the program would make it possible for all low-income families to obtain more child care

A．The average family with children under age four spends more than $1,000 a year on child care.

B．Some low-income families in which one of the parents is usually available to care for children under age four may not want to spend their income tax refund on child care.

C．The reduction in government revenues stemming from the income tax refund will necessitate cuts in other government programs, such as grants for higher education.

D．Many low-income families with children under age four do not pay any income taxes because their total income is too low to be subject to such taxes.

E．(E) Income taxes have increased substantially over the past twenty years, reducing the money that low-income families have available to spend on child care.
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