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问题 选择题

从A={a1，a2，a3，a4}到B={b1，b2，b3，b4}的一一映射中，限定a1的象不能是b1，且b4的原象不能是a4的映射有（　　）个．

A．12

B．13

C．14

D．16

答案

a1的象不能是b1，分两种情况：

①a1的象是b4，a4的象有3种选择，其它两个元素的象分别有2和1选择，共3×2×1=6；

②a1的象不是b4，有两种选择，a4的象也有2种选择，其它两个元素的象分别有2和1选择，

共2×2×2×1=8．

∴总计6+8=14．

故选C．

单项选择题 A1型题

营养性贫血的有效治疗措施是（）

A.叶酸加维生素B12

B.硫酸亚铁加维生素C

C.反复多次输血

D.服枸橼酸铁胺

E.肌内注射右旋糖酐铁
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单项选择题

Because the process of freezing food consumes energy, many people keep their electric freezers half-empty, using them only to store commercially frozen foods. Yet freezers that are half-empty often consume more energy than they would if they were kept fully stocked.
Which of the following, if true, contributes most to an explanation of the apparent discrepancy described above ？（）

A．A given volume of air in a freezer requires much more energy to be maintained at a temperature below freezing than does an identical volume of frozen food.

B．The more often a freezer’s door is opened, the more energy is required to maintain that freezer’s normal temperature.

C．When unfrozen foods are placed in a freezer, the average temperature of a given volume of air inside that freezer rises temporarily.

D．A person who normally maintains a half-empty freezer can cut energy costs considerably by using a freezer that is 50 percent smaller.

E．An electric freezer can operate efficiently only if chilled air is free to circulate within the freezing compartment.
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