若Sn是数列{an}的前n项和,且Sn=n2则{an}是( ) A.等比数列,但

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问题:

若Sn是数列{an}的前n项和,且Sn=n2则{an}是(  )

A.等比数列,但不是等差数列

B.等差数列,但不是等比数列

C.等差数列,而且也是等比数列

D.既非等比数列又非等差数列

考点:等差数列的定义及性质
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因特网的主要组成部分包括通信线路,路由器,______和信息资源。

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防止职业病发生的根本措施是()

A.加强健康教育

B.做好卫生保健工作

C.加强毒物的安全保护工作

D.合理使用个体防护用品

E.将生产环境有害因素浓度或强度控制在职业接触限值以下

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下列有关溶血性贫血的叙述,哪项是正确的()

A.可能存在红细胞内在缺陷

B.红细胞寿命缩短

C.可能存在红细胞外在异常

D.脾脏功能亢进

E.以上都是

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高频开关电源设备应能监视电网电压,过压保护电压的设定不应低于额定电压值的(),欠压保护电压的设定不应高于额定电压值的()。

A.100%;50%

B.110%;60%

C.115%,80%

D.130%;100%

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Throughout history has (1) changed his physical environment in order to improve his (2) of life. With the tools of technology he has (3) many physical features of the earth. He has (4) woodlands and prairies into farms and made lakes and reservoirs (5) of rivers for irrigation purposes or hydroelectric (6) . Man has also modified the face of the earth by (7) marshes and cutting through mountains to (8) roads and railways.
However, man’s (9) to the physical environment have not always had beneficial results. Today, (10) of the air and water is an increasing danger to the health of the (11) . Each day thousands of tons of gases come out of the exhausts of motor vehicles. (12) from factories pollutes the air of industrialized areas and the surrounding (13) of the countryside. The pollution of water is equally harmful. The whole ecological (14) of the sea is being changed and (15) wastes have already made many rivers lifeless.
Now (16) protection is more pressing than ever before. As we know, massive destruction of the environment has brought about (17) effects and even poses a great (18) to man’s existence. Indifference to these problems will mean committing suicide. Therefore, effective (19) should be taken and laws passed to (20) the environment. Otherwise, man is certain to suffer from the serious consequences caused by this lack of care for his living surroundings.

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