题目

在“证明大气压存在”的活动中，小科同学完成了“快速使易拉罐变瘪”的实验，实验过程如下：在易拉罐中添加少量的水，用酒精加热至沸腾（如图所示），当罐口有水汽逸出时，迅速将易拉罐开口朝下倒扣在冷水中（如图所示），易拉罐骤然变瘪。请你用所学知识对此现象做出解释？ 答案：加热时易拉罐中水汽化，当罐中充满水蒸气，大部分空气被排出易拉罐，此时将易拉罐迅速倒扣在冷水中，罐内水蒸气遇冷液化，罐内气压变小，小于外界大气压，在大气压的作用下将易拉罐压瘪阅读短文，根据短文内容．从短文后的六个选项中选出能填入空白处的最佳选项。选项中有一项为多余选项。It’s hard when a best friend isn’t around—maybe because she moved to a different school or a different class, or maybe she’s just sick at home for the day. Break or lunchtime can be lonely without her. Will it ever feel the same? 1. , but how do you make them? Maybe it seems like everybody else already has their friends. But remember, there’s always room for more friends.Start by looking around your classroom—think about which one you’d like to play with at break.Look for chances to say hi to them, smile, and be friendly. Offer to share something or offer greetings. Invite someone to play with you or say “Do you want to sit here?” in the lunchroom. 2. , walk over to the ones you want to play with,act friendly, and say “Hi, can I play, too?” or just join in.3. ,or if you’re feeling shy, ask your teachers to help you to make new friends. Teachers are usually pretty good at matching up friends. The best way to make friends is to be a friend. 4. .As a result, you’ll soon have one, or two, or even more new friends.You might still miss that special best friend. 5. , you can share something you didn’t have before she left: You can introduce her to your new friends!A. When you are at lesson breakB. If you have trouble doing thisC. You want to have new friendsD. But when you see each otherE. And you’ll be happy with themF. Be kind, be friendly, offer to help