题干

下列关于细胞增殖的叙述正确的是( )

A:着丝点分裂一定导致DNA数目的加倍

B:合适观察细胞有丝分裂的是蚕豆根尖分生区细胞

C:有丝分裂中期,细胞中染色体数是体细胞染色体数的两倍

D:细胞体积越小,细胞的表面积越大,细胞与周围环境进行物质交换的效率就越大

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B

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    Sometimes I have to admire people's imagination but what I admire most is the businessmen's sense of smell. China's Singles Day, which falls on Nov. 11 every year, has far surpassed its U.S. counterparts of Black Friday and Cyber Monday—combined. Last year, Americans spent a record $12.8 billion online between Thanksgiving Day and Cyber Monday. It's impressive until you compare it to the $17.6 billion in sales made by Chinese consumers in a single 24-hour period during 2016's Singles Day.

    Singles Day is known as “Bare Sticks Day” or “Bare Branches Day” in Chinese—because the date “11/11” looks like bare branches and “one” is the loneliest number. Singles Day began in the early 1990s in the dorm rooms of Nanjing University when a group of single friends were sorry about the lack of significant others and decided to mark the day by organizing activities as a group of singles and reducing their loneliness by buying themselves a gift.

    Then in 2009, sensing s break between the sales period of China's National Day on Oct. 1 and Chinese New Year in late January or early February, Alibaba's Jack Ma saw an opening: sell to comfort lonely hearts.

    The first year did only $7.5 million in sales, but just 8 years later, shoppers spent $25.3 billion, or 168.2 billion yuan, this year—a 40 percent jump from last year's $17.6 billion. Foe comparison, Black Friday and Cyber Monday in the U.S. only netted $6.79 billion in 2016. Amazon doesn't release sales figures for July's Prime Day, but it's pretty safe to believe the not-quite-national-holiday doesn't come close to $25 billion.

    “More than $25 billion in one day is not just a sales figure,” Alibaba Group CEO Daniel Zhang said in a statement. “It represents the desire for quality consumption of the Chinese consumer, and it reflects how merchants and consumers alike have now fully accepted the combination of online and offline sales.”