For years, people have wondered whether there's life on other planets. Scientists may now be closer than ever to answering that question.

    Using powerful telescopes, a team of astronomers in South America discovered a new planet, called Proxima b. It circles a star named Proxima Centauri, in the same way Earth circles the sun. Proxima Centauri is the closest star to our solar system.

    Scientists believe the new planet has a rocky surface and is similar in size to Earth. More important, they've determined that the distance between Proxima b and its “sun” gives the planet a similar temperature to Earth's.This means it could have liquid water. The presence of water on a planet makes it possible for life to exist there. Scientists refer to planets like Proxima b as “Goldilocks planets” because they are not too hot or too cold, but just right to possibly support life.

    Astronomers have found other Goldilocks planets in the past, but none are as close to Earth as Proxima b. Still, the new planet is 4.2 light years from Earth—that is about 25 trillion miles away.

    Despite the long distance, astronomers hope to get a much better look at our new-found neighbor one day. But they'll need to wait until more advanced telescopes are developed. They may also send a robotic spacecraft to investigate the planet.

咖啡是一种热带经济作物。以下国家中，最适宜种植咖啡的是（　　）

已知方程组$\left\{\begin{array}{c}2x+y=4\\ x+2y=5\end{array}\right.$，则x+y的值为____ 

根据短文内容，选择正确答案。

    Tom walked into a shop. It had a sign outside: “Second-hand (旧的）clothes bought and sold.” He was carrying an old pair of trousers and asked the owner of the shop, “How much will you give me for these?” The man looked at them and then said,“Two dollars. ”

  “What?!” said Tom. “I thought they were worth at least five dollars.”

  “No,” said the man “They aren't worth a cent more than two dollars.”

  “Well,” said Toni, taking two dollars out of his pocket. “Here's your money. These trousers were hanging outside your shop. The list price (标价）of them was six dollars and a half. But I thought that was too much money, so I wanted to find out how much they were really worth.”

    Then he walked out of the shop with the pair of trousers and disappeared before the shop owner could think of anything to say.

下列句子的关联词使用不正确的是（    ）