AaBb 1AB：1Ab：1aB：1ab 配子间16种结合方式 子代中有9种基因型 4种表现型（9：3：3：1）

    If you are studying at school, do be a polite and clever student! There is no excuse for not doing your assignments. If you can't come to school, you should call your teacher or your classmate ask about homework. It is your responsibility to find out what homework you have missed. It is not the teacher's job to remind you of the missed assignments.

    You must not be absent on a test day. If you are seriously ill, call and let the teacher know you will not be there for the test. If your teacher allows a make-up test, you should take the test, again within one or two days after you return to class. Serious illness is the only reason for missing a test.

    Be on time! It is impolite to be late. Also, it bothers other students. If you must come in late, be sure to do it quietly. Have your books and papers out of your bag before you come into the classroom. Then go to your seat and sit down quietly. In the USA, it is not necessary to knock before you enter the classroom. Most teachers will give you a low grade if you are often late.

    In America, you should call your teacher by his or her last name instead of “teacher”. Also you should use Mr, Miss, Ms or Mrs before the last name (such as Mrs Smith or Mr Jones). The teacher will tell you the title that he or she likes. It is impolite in the USA to eat, drink or chew gum during class. Don't do these until the break. Also, removing your shoes in the classroom is not polite.

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冰的体积变大还是变小？

在物理小组活动的时候，小明提出了这样一个问题：“水在结冰的时候体积如何变化？”小刚立即做出了回答：“根据物体热胀冷缩的性质，水结冰时的体积当然是变小的。”但小红提出了相反的意见：“如果体积变小的话，那么冰的密度会变大，冰将会沉入水中。但事实上冰会浮在水面上，所以体积应变大。”

到底谁对谁错呢？小刚提出了通过实验去解决这个问题，并提出了自己的实验方案：“在小药瓶中装满水，放到冰箱中使水完全凝固，然后看看冰面是下降了还是升高了，不就行了吗？”大家都赞同这个方法，于是他们立即动手实验。于是他们在小容器中装满水后放入冰箱让它结冰，结果发现冰面是向上凸起的。

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