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问题 选择题

根据下列金属与盐溶液发生的置换反应，判断X、Y、Z三种金属单质的活动顺序是

①Z+YSO4→ZSO4+Y   ②X+YSO4→XSO4+Y   ③X+Z（NO3）2→X（NO3）2+Z（　　）

A．X＞Y＞Z

B．Z＞Y＞X

C．Z＞X＞Y

D．X＞Z＞Y

答案

Z+YSO4→ZSO4+Y，说明Z＞Y，X+YSO4→XSO4+Y，说明X＞Y，X+Z（NO3）2→X（NO3）2+Z，说明X＞Z，所以其顺序为X＞Z＞Y，故选D．

判断题

煤矿企业按照国家法律、法规和卫生行政主管部门的规定，不定期为接触粉尘、毒物及有害物理因素等的作业人员进行职业健康检查。
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单项选择题

When a disease of epidemic proportions threatens the public, scientists immediately get to work, trying to locate the source of affliction and find ways to combat. Vaccination is one of the effective ways to protect the (1) population of a region or country which may be (2) grave risk. The process of vaccination allows the patient’s body to (3) immunity to the virus or disease so that, if it is encountered, one can fight it (4) naturally. To accomplish this, a small weak or dead (5) of the disease is actually injected into the patient in a controlled environment, (6) his body’s immune system can learn to fight the invader (7) . Information (8) how to penetrate the disease’s defenses is (9) to all elements of the patient’s immune system in a process that occurs naturally, in which genetic information is passed from cell to cell. This makes sure that (10) the patient later come into contact with the real problem, his body is well equipped and trained to (11) with it, having already done so before.

There are, however, dangers (12) in the process. (13) , even the weakened version of the disease contained in the vaccine proves (14) much for the body to handle, resulting in the immune system (15) , and, therefore, the patient’s death. Such is the case of the smallpox vaccine, (16) to eradicate the smallpox epidemic that nearly (17) the whole Native American population and killed massive numbers of settlers. (18) 1 in 10,000 people who receive the vaccine (19) the smallpox disease from the vaccine itself and dies from it. Consequently, the process, which is truly a (20) , may indeed hide some hidden curses.

3（）

A.eliminate

B.identify

C.develop

D.deliver
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