题干

下列说法正确的是(   )

A:做曲线运动的物体加速度可能为零

B:平抛运动的物体在任意相等时间间隔内的速度改变量相同

C:一个匀速直线运动与一个匀变速直线运动合成后一定是曲线运动

D:做匀速圆运动的物体受到的合力一定沿半径指向圆心

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B,D

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    From Dusner (3 speakers) to Kelabit (5 thousand) to Yiddish (1.5 million), these languages are spread, but like the Indian elephant, they are in danger of dying out. Dr. Chris Mazdzer, a researcher at Oxford University, organizing a meeting on endangered languages thinks there could be a novel way to keep minority languages alive: social media. He says, “Because young people text each other how they speak, even if they don't know how to spell it.”

    Minority languages are often at risk of being drowned(淹死)out by the bigger ones, which are spoken at school and in the media. But the appearance of Facebook and Twitter might just have the unexpected effect. Dr. Mazdzer speaks Frisian, which has 350,000 speakers. Communicating with his own language has given him thought about how languages could be saved in the future. “In Friesland, young people who don't learn much Frisian at school send each messages on social media in Frisian”, he says. In this way, a new generation of Frisian speakers keeps the language alive.

    Though many of these languages only have a few speakers, it's not just a small number of speakers that make a language endangered. Some languages were once widely spoken, but lost speakers over time. This can happen for many reasons, like only one language spoken in school or people moving away from their home and losing their language.

    Tweeting and texting in Frisian (or Sorbian, or Breton) is not enough in the long term, though. There are many other things we need to do. But why is a language worth saving in the first place? Because our languages are natural creations. Natural beauty needs to be protected.