题干

如图甲所示,一块长木板放在水平桌面上,现用一水平力F1向右缓慢地推木板,使其一部分露出桌面,如图乙所示,在推木板的过程中木板对桌面的压力F、压强p和摩擦力f的变化情况是(  )

A:F、p不变,f变大

B:F、f不变,p变大

C:F变小,p、f变大

D:F、f不变,p变小

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答案(点此获取答案解析)

B

同类题2

阅读下列短文,从各题所给的四个选项(A B C D)中,选出最佳选项。

B

    Do you shop online with websites like Taobao? The money you pay doesn't go directly to the seller. Instead, it goes through Alipay, which keeps your money for a while. After you receive your goods and click the "confirm receipt" button, Alipay then gives the money to the seller.

    The process is called "third party online payment". There is a transfer station, or a third account, between sellers and buyers to make online shopping safe. Buyers don't need to worry about paying for goods and then receiving nothing. Sellers also get rid of the risk of receiving no money after sending out goods.

    These transfer stations are usually set up by payment service companies such as Alipay, Tenpay and Yeepay. Among them, Alipay is the biggest in China. It has more than 270 million active users, according to Xinhua.

    While most online sellers and shoppers like the third party online payment system, banks are not very happy. That is because companies like Alipay are fighting over money with the banks. Users can invest in financial products through Alipay and make money. Thus lots of people choose to put money in Alipay rather than in banks.

    But WeChat payment is not the same. WeChat doesn't have its own account. When paying through WeChat, the buyers' money goes directly to the sellers. That's why so many people are excited about receiving and handing out "red envelopes" or gift money to their friends on WeChat.

    Whether Alipay or WeChat payment, they are all trying to attract more users and make online shopping easier. These two companies are also promoting payments through fingerprints. New payment methods such as quick response codes have become popular too.