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高速公路上的标牌常用“回光返照膜”制成,夜间行车时,它能将车灯照射出去的光逆向返回,标志牌上的字特别醒目。这种“回光返照膜”是用球体反射原件制成的.如图所示,反光膜内均匀分布着直径10um的细玻璃珠,所用玻璃的折射率为√3,为使入射的车灯光线经玻璃珠折射、反射、再折射后恰好和入射光线平行,那么第一次入射的入射角是

A:

B:

C:

D:

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D

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    England continues to be one of the most popular tourist destinations in the world. London in particular is one of the most visited cities and draws people in with its appeal, history, and pubs. England's smaller cities, like Bath and Oxford, are equally as attractive with a lot of culture and fewer crowds. Liverpool, birthplace of The Beatles, has a rich musical history. The countryside has wonderful natural beauty. Here are some tips on traveling in England.

    Free museums—Public museums offer free admission in every city throughout England and the UK. It's a great way to learn about the country's most influential artists and history, and spend a rainy day without paying a cent.

    Book early—Book all transportation well in advance, even if you don't plan to use it. Fares can be around £2 with a little planning. The Megabus not only runs buses but also provides trains throughout England and is the best choice for cheap travel throughout the country.

    Pub food—Eating in England can be quite expensive, but for good cheap and filling meals, visit the local pubs, where you can get a good meal for less than £10. Besides, the pubs are a great way to meet people!

    Get a Taste of UK card—The Taste of the UK card offers up to 50% off at selected restaurants. You don't need to be an English to get the card, and you needn't pay the first month's membership fee, which is perfect for most travelers.

    Take a free walking tour—Many major cities in England offer free walking tours. They usually last a few hours and are a great way to see the city.