题干

图为广州亚运会奖牌(海上丝路) 的正面,有人在解读其设计时说“如果不写广州的海上丝绸之路,中国古代海上丝绸之路的历史就支离破碎,暗然失色,不堪入目。”以下关于古代广州对外贸易历史的表述不正确的是

A:西汉时期,广州作为海上丝绸之路的发源地,是重要的对外贸易港口

B:唐朝时,政府在广州设立市舶使管理对外贸易

C:元朝时广州是对外贸易的重要港口,被誉为当时世界第一大港口

D:清代政府实行闭关锁国政策,只特许广州的“十三行”统一经营对外贸易

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答案(点此获取答案解析)

C

同类题5

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                                                                           C

    Flying is a fast way to travel. But it is a big headache for some people. They can't help worrying about things like, “Is turbulence (颠簸) a bad thing?” or, “Is it dangerous if we don't change our mobile phones to flight mode (飞行模式)?” British newspaper Daily Mail spoke to some experts to answer these questions. They also tell us other interesting things about flying.

    Is turbulence dangerous?

    It's scary and uncomfortable. But it is not something you really need to worry about.

    Turbulence is caused when two groups of air hit one another at different speeds. Wind, thunderstorms (暴风雨) and being close to mountains can be reasons for this.

    You may feel like turbulence is dangerous, but it won't crash (坠毁) your plane. “Even in extremely rough air (扰动气流), the wings (机翼) are not going to break off,” explained Patrick Smith, an airline pilot, who is also an air travel blogger and author of Ask The Pilot. com.

    Why are plane windows round?

    Round windows are for passenger safety.

    As the airplane flies higher and higher, the outside atmospheric pressure (气压) gets lower and lower. During the flight, the pressure inside the plane becomes greater than the pressure outside.

    When this happens, square windows can break. That's because having different pressures inside and outside puts pressure on the corners of square windows. But rounded corners can spread the pressure through the window.

    What happens when a phone isn't on flight mode?

    Some passengers believe mobile phones and tablets need to be turned off because they could bring the plane down. However, this is not true.

    If you don't change your phone to flight mode, pilots and air traffic controllers may hear unpleasant sounds in their headphones. It also influences radio communications. So it's still best to put it on flight mode.