You probably know you should say “please” and “thank you” at restaurants. You probably know the rules of a library. You know you should respect(尊重) and be nice to your classmates. But do you have music manners?
   Keep It Down! You have to notice the volume of your music. You should not play your music so loud that everyone around you can hear it. Some people might even get angry. Usually, when you play the music loud on an MP3 player, other people can't hear the words of the song. They just hear a loud sound. No one wants to listen to this. Very loud music can also be bad for your ears, so even if you are alone when listening to your MP3 player, you shouldn’t have it turned up too high.
   Take Them off! You need to know when to turn your MP3 player off and put it away. Libraries and schools don't allow MP3 players. There are other places, like museums, that don’t have rules, but it would be rude to have your MP3 player on. Why would you listen to music at a play, a movie or a sporting event? You would miss what is going on and others would wonder why you even came.
   Take One Out! Once in a while it's OK just to take out one earphone and not the other. Imagine you are listening on your MP3 player when someone asks you the way. It would not be rude to take out one earphone, tell him the way, and put back the earphone and continue listening. You can also do this when you order food at a fast-food restaurant or when you answer the telephone and it's not for you.
   It’s Your Choice! There are times when you need to decide what is best. For example, some people can listen to music on their MP3 players when reading books, while others think it is disturbing. In cases like this, you need to do what seems right for you.

二面角α﹣l﹣β的半平面α内有一条直线a与棱l成45°角，若二面角的大小也为45°，则直线a与平面β所成角的大小为____ 

阅读下面的文字，按要求完成两小题。

    以《城市剪影》为主题的灯光小品秀将在西湖边拉开帷幕。这次灯光小品设在湖滨路步行街，虽然仅仅只有100多米，却是西湖边最热闹的去处之一。一直要持续到10月25日，在每晚的日落时间至21：30亮灯。

     _____________________。比如，步行街会设置一幅名为“印·像”的灯光墙，使用投光灯投影于幕布上，游客站在幕布前，即可在墙后留下自己的“剪影”。这个形似外墙的作品，据设计师介绍灵感来源于城市的窗户。每一个窗户背后都有一个故事，所有的故事汇聚而成一个城市的生命与记忆。游客可以在窗户后摆出自己的特有的姿势，留下自己的“剪影”。

（内容来自2015年10月16日  《都市快报》）