阅读下列短文，从每题所给的四个选项中，选出最佳选项。
C
    There are an extremely large number of ants worldwide. Each individual ant hardly weigh anything, but together they weigh almost the same as all of mankind. They also live nearly everywhere, except on frozen mountain tops or around the Antarctic. For animals their size, ants have been surprisingly successful, largely due to their wonderful social conduct.
    In groups that vary in size from a few hundred to tens of millions, they organize their lives with a clear distribution of labor. Even more amazing is how they achieve this level of organization. While we use sound and sight to communicate, ants depend mostly on pheromone (信息素), which is a kind of chemical released by individuals and smelled or tasted by fellow members of a group. When an ant finds food, it produces a pheromone that will lead others straight to where the food is. When an ant comes under attack or is dying, it sends out an alarm pheromone to warn the whole group to prepare for a defensive fight.
    In fact, when it comes to the art of war, ants have no equal. They are completely fearless and will take on an animal much larger than themselves, attacking in large groups and beating their target. They show so much devotion to their group that not only soldier ants but also worker ants will sacrifice their lives to help defeat an enemy.
    United and devoted, these little animals have survived on the earth for more than 140 million years, far longer than dinosaurs. Because they think as one, they have a united intelligence greater than you would expect from one small individual ant.

 Can you hear a duck? Yes.

已知y是x的一次函数，当x=3时，y=1；当x=﹣2时，y=﹣4，求这个一次函数的解析式．

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.

下列四种现象中，能用来说明分子间存在引力的是 （   ）