B

    We are learning English, but how can we learn English well? A student can know a lot about English, but maybe he can't speak English.

If you want to know how to swim, you must get into the river. And if you want to be a football player, you must play football.

    So you can learn English only by using it. You must listen to your teacher in class. You must read English every day. You must speak English to your classmates and you must also write something in English sometimes. Then one day, you may find your English very good.

如图所示，请根据已知光线，完成光路图．

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公元1500年左右，欧洲出版了大约4万册图书，极大地激发了民众的求知欲。此种情形直接得益于