题干

某次军事演习中,红方飞机甲正从北向南水平匀速飞行,飞行员发现其正前方距离x处有一架蓝方飞机乙正从东向西水平匀速飞行,随即水平发射炮弹,炮弹的发射方向与飞机的飞行方向成?角,经过时间t炮弹击中飞机乙。已知飞机甲的速度为v1,乙的速度为v2,甲在地面上静止时发射炮弹的速度为v0。忽略炮弹竖直方向的位移和所受的空气阻力。则下列说法中正确的是

A:

B:

C:

D:

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C

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     World Book Day falls on April 23 every year. It was set up by the UNESCO(联合国教科文组织) in 1995 to encourage people, especially teenagers, to discover the pleasure of reading. It is also the day to honor great writer, for example, William Shakespeare, born or dead on that day.
       Many countries celebrate World Book Day. Take UK as an example. On that day, millions of school children can buy books of special price, a much lower price than usual, in any bookstore. It has been done every year since 1998. World Book Day is also celebrated in China. Premier Wen Jiabao does lots of reading every day. Wen has called on people to do more reading. He suggested that young people should spend more time reading. “Book cannot change the world, but people can change the world by changing themselves through reading,” he said.
    Why do people like reading? One big advantage is that reading helps us become more knowledgeable and more intelligent. Also, reading helps us to follow the latest developments of science and technology. Besides, reading gives us information about other cultures and places of the world. When we read, we may find many things that are unfamiliar to us. We would have to use our brain to think about them or do more reading to find out the answers. The more we read, the more we know. What's more, reading is also one of the most important ways to learn a foreign language like English.
   “Reading makes a full man”. Books, magazines, newspapers and other kinds of materials can help us to know more about the outside world and perf