什么叫定滑车、动滑车和滑车组?

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问题:

什么叫定滑车、动滑车和滑车组?

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父子二人在一条长800m的环形跑道上跑步晨练,父亲的速度是200 m/min,儿子的速度是150 m/min,两人从相距200的位置同时同向跑,并且父亲在前面,儿子在后面,问第一次相遇时父亲共跑了多少米?

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Pharming is a scamming practice in which malicious code is installed on a personal computer or server, misdirecting users to (1) Web sites without their knowledge or consent. Pharming has been called "phishing without a lure".

In phishing, the perpetrator sends out legitimate-(2) e-mails, appearing to come from some of the Web’s most popular sites, in an effort to obtain personal and financial information from individual recipients. But in pharming, larger numbers of computer users can be (3) because it is not necessary to target individuals one by one and no conscious action is required on the part of the victim.In one form of pharming attack, code sent in an e-mail modifies local host files on a personal computer. The host files convert URLs into the number strings that the computer uses to access Web sites. A computer with a compromised host file will go to the fake Web site even if a user types in the correct Internet address or clicks on an affected (4)entry. Some spyware removal programs can correct the corruption, but it frequently recurs unless the user changes browsing (5)

4()

A.hypertext 

B.computation 

C.expectation 

D.bookmark

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三个好朋友“五一”节准备外出游玩,他们对出行方式的态度如下:王某要坐车,什么车都可以:李某可以不坐车,要坐就坐公交车;张某可以不坐车,要坐就坐出租车。如果他们根据自己的态度,对以下意见表示自己的看法:不坐车;坐公交车,坐出租车。
根据以上资料,以下哪项是不可能成立的( )

A.有一个人同意全部意见

B.每个意见至少有两个人同意

C.王某和李某都同意坐公交车

D.张某同意不坐车和坐出租车

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心房颤动患者服用华法林,凝血酶原时间的国际标准化率(INR)应控制在  A.

A.1.0~ 1.9

B.2.0~ 3.0

C.3.1~ 3.5

D.3.6~ 4.0

E.>4.0

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效应T细胞的作用最完整的一组是()

①分泌抗体

②呈递抗原

③识别抗原

④激活溶酶体酶

⑤与靶细胞结合

A.③④⑤

B.①②③⑤

C.②③④⑤

D.①②③④

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