题干

如图所示,P、Q是两种透明材料制成的两块直角梯形的棱镜,叠合在一起组成一个长方体。某单色光沿与P的上表面成θ角的方向斜射向P,其折射光线正好垂直通过两棱镜的界面。已知材料的折射率nP<nQ,则下列说法正确的是

A:一定没有光线从Q的下表面射出

B:从Q的下表面射出的光线一定与入射到P的上表面的光线平行

C:如果光线从Q的下表面射出,出射光线与下表面所夹的锐角一定大于θ

D:如果光线从Q的下表面射出,出射光线与下表面所夹的锐角一定小于θ

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答案(点此获取答案解析)

D

同类题4

根据短文理解,选择正确答案。

    A news release (释放,发布)is a tool of communication,through which information is passed to even the farthest end of the world.It keeps us well informed of the happenings of the world which would otherwise remain unknown.

    When writing a news release,keep in mind that the media receive hundreds of releases every day.Try to follow these guidelines:Keep it short and professional.Come up with a catchy headline that will grasp someone's attention.Sometimes the title will take more time to come up with than writing the release.That's okay-the headline could be critical for getting an event covered!

    Cover the 5 W's in your first paragraph.Those are who you are; what you are doing;where,when you are doing;why you are doing it,which help us understand the details about the event.Besides,any opinions in the news release should be put in quotations from your designated spokesperson.Include things that the media finds newsworthy,which is the most essential.

    Make the time on your news release at least half an hour later than the time you have told activists to show up at an event.This will ensure that activists are prepared and in place by the time the media arrive.

    Choose a spokesperson for the event who can be quoted in the release and will be available for calls at that number the day before the event.

    Have someone proof the release for spelling,grammar and content (determine whether what you are trying to relay is clear and right).Sometimes the person who writes the release may not notice mistakes that a fresh pair of eyes will catch.

    Accuracy is the last but not least important in terms of your content and the location and time that you tell the media.If you do make a mistake,it is critical that you call and notify the media of the correction.