题干

一列简谐横波,A为振源,在B点刚开始振动时的图象如图所示.图中数据单位都是m,已知波的传播速度为10m/s,下列说法正确的是_________(填入选项前的字母代号)

A:振源A开始振动时的速度方向向下

B:从振源A开始振动到形成如图所示波形,经过时间为1.6

C:此后再经过0.2s,振源A到达波峰

D:从M点开始运动到如图所示时刻,M通过的路程为1.0m

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答案(点此获取答案解析)

B

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    We all dream about things that we would like to do and things we hope to achieve in the future. But are everybody's dreams the same? Here are some of the findings of a survey about hopes and dreams,and thousands of students across China took part in it.

    What are the hopes of teenagers?

    We received several different answers to the question:What would you like to do after finishing your education? It seems some students would like to start work as soon as possible, so that they can help provide better lives for their parents. Other students hope to continue studying after finishing school and to go to university. Although money is important, many teenagers said they want to do jobs they enjoy. According to the survey, the most popular choice of job is computer programming.

    What are the dreams of teenagers?

    Teenagers have all kinds of dreams. Some are more realistic(现实的) than others. For example, many students said they would like to be volunteers if Beijing could hold the World Cup, maybe working as translators or tour guides. And quite a few said they dream of going to the moon one day. According to the survey, less realistic dreams are also common, but many students reported that they were willing to work hard to achieve their dreams. Quite a few dream of becoming famous, perhaps famous sports people or singers. Some said they'd like to go on exciting trips; one student said she'd love to sail across the Pacific Ocean. And then there are dreams that are impossible; three students said they'd like to be able to fly!

    Conclusion

    It was clear from the survey that teenagers have similar hopes. It seems that most students hope to have a good education and find a good job. Besides,students dream of very different things:good things, and even crazy things. It is very important to dream, so hold on your dreams; one day they may just come true.