如图所示,AB是一质量为m的均匀细直杆,A端靠在光滑的竖直墙壁上,B端置于水平地

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问题:

如图所示,AB是一质量为m的均匀细直杆,A端靠在光滑的竖直墙壁上,B端置于水平地面上,杆身与竖直方向夹角为θ,杆与地面的摩擦系数为μ,保持平衡,则此时杆与地面的摩擦力为(  )

A.mgtgθ

B.mgsinθ

C.μmg

D.μmg

考点:摩擦力的大小摩擦力的种类杠杆的平衡条件
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汽车变速器由()和()两部分组成。

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阅读理解。

     Restaurant owners should not use disposable chopsticks for the good of their health and the

environment, an official of the China Cuisine Association (中国烹饪协会) said.

     Bian Jiang, its secretary general, recently called on restaurant owners to say no to one-off tableware

(餐具), especially wooden chopsticks. "The country produces and throws away over 45 billion pairs of

wooden chopsticks every year, at a cost to the environment of about 25 million tree." Bian said.

      "That's a heavy blow to the county's shrinking forests," he said, "We should not turn a deaf ear to the

call for environmental protection. We should stop using disposable tableware from now on."

      In order to discourage the use of wooden chopsticks and to protect wooden resources, the government

put a 5% tax on them in April.

     The use of disposable chopsticks has been discussed for years. Their supporters say that both restaurant

owners and consumers prefer them, and that an industry has grown up around their production.

1. The secretary general suggests that wooden chopsticks be stopped from being used because _____.

A. they cause a lot of pollution of the environment

B. the environment is no longer green

C. the government is not happy with that

D. too many trees are cut

2. From the text we know that the idea of no disposable tableware will be _____.

A. hard to put into practice

B. welcomed by a lot of people

C. receiving indifferent attitudes

D. rejected by some people

3. What does the underlined word "disposable" in the first paragraph mean?

A. Waste

B. Expensive

C. Man

D. One-use

4. What's the main idea of the text?

A. Many people support the idea of saying no to using wooden chopsticks.

B. The government calls on people to stop using wooden chopsticks.

C. Disposable tableware wastes a lot of forests and does damage to the environment.

D. People are aware of the cost of using disposable tableware.

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患者吐血缠绵不止,时轻时重,血色黯淡,神疲乏力,心悸气短,面色苍白,舌质淡,脉细弱。其治法是()

A.健脾和胃,宁络止血

B.和中宁络,凉血止血

C.益气养阴,宁络止血

D.健脾益气,摄血止血

E.健脾升阳,化瘀止血

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岩石是一种或几种矿物组成的开然集合体,其种类很多,按其成因可分成哪三大类?另外,第四纪以来经各种地质作用形成未硬结成岩的堆积物,统称为什么?

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根据有关规定,银行通过互联网为个人客户办理电子支付业务,除采用数字证书、电子签名等安全认证方式外,单笔金额和每日累计金额分别不应超过一定数额。该数额为( )。

A.单笔金额不得超过500元,每日累计金额不得超过2000元
B.单笔金额不得超过10130元,每日累计金额不得超过5000元
C.单笔金额不得超过2000元,每日累计金额不得超过5000元
D.单笔金额不得超过10000元,每日累计金额不得超过 20000元

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