问题 选择题

潜水员在水面下不断下潜的过程中,受到的压强和浮力的变化情况是(  )

A.压强不变,浮力变大

B.压强变小,浮力变小

C.压强变大,浮力不变

D.压强变大,浮力变大

答案

潜水员在水面下不断下潜的过程中,水的密度ρ不变,

∵F=ρVg,排开水的体积不变,

∴潜水员受到的浮力不变;

∵p=ρgh,潜水员所处的深度h变大,

∴潜水员受到的水的压强变大;

故选C.

阅读理解

“It is one of the few bright spots in the Chinese economy,” says Zeng Ming. He is talking about e­commerce. Mr. Zeng, the chief strategy officer for Alibaba, a giant Chinese Internet firm, predicts that digital transactions on his firm's platforms will top 1 trillion yuan($159 billion) this year—more than Amazon's and eBay's combined. That is a bold claim, but consider what happened on Singles Day.

Invented a few years ago by students and seized upon by digital marketers, this festival for lonely hearts falls annually on the 11th day of the 11th month(since 1 is the loneliest number). It is like St Valentine's Day, only worse. Singletons show each other with tender gifts: a barrage of pearls; a storm of sweets.

This November 11th they spent a surprising 19 billion yuan on Alibaba's online platforms—a fourfold increase on a year ago, and more than double what Americans spent online last Cyber Monday(the Monday after Thanksgiving, when retailers urge Americans to shop online). About 100 million purchases were logged, accounting for 80% of the packages shipped that day. Couriers(快递员) were buried in parcels.

So life is good for China's e­tailers. Then? Not exactly. The number of digital marketers is increasing and online sales are booming. Consumers are enjoying lower prices, better service and more variety. The problem? The pressure on profits in Chinese e­commerce is worse than in America, reckons Elinor Leung of CLSA, a broker. “Almost no one makes money,” she says.

The fiercest battles are being fought between online retailers and their bricks­and­mortar(实体的) rivals. Dangdang, a firm that resembles Amazon, and 360buy, another online retailer, have cut prices fiercely. Tencent, a cash­rich online giant known for its instant­messaging software, is splashing out to win market share. 360buy has also just raised $400 millon from investors to do the same. But it is unclear how much longer such firms can burn through capital.

小题1:What's the best title of this passage?

A.The Ambition of Alibaba

B.Fierce Competition between Retailers

C.A New Festival for the Singles

D.Chinese Booming E­commerce小题2:According to Zeng Ming, this year Alibaba will ________.

A.outweigh Amazon and eBay in worldwide influence

B.rank top among all the Internet firms

C.have more than 159 billion dollars' sale

D.create another sales miracle just like the one on Singles Day小题3:How many packages were shipped on November 11th from Alibaba's online platforms?

A.About 80 million.

B.About 100 million.

C.About 125 million.

D.About 180 million.小题4:What's the author's attitude towards online retailers in China?

A.Optimistic.

B.Concerned.

C.Sympathetic.

D.Indifferent.

单项选择题