阅读理解。 Here are some American classroom customs : If the teacher asks a question, you are expected to give an answer. If you do not understand the question, you should put up your hand and ask the teacher to repeat the question. If' you do not know the answer, it is all right to tell the teacher that you do not know. Then he or she knows what you need to learn. There is no excuse for not doing your homework.  If you are absent (缺席的) ,  you should call your teacher or someone who is in your class and ask about the assignment(作业).  It is your responsibility(责任)  to find out what the assignments you have missed are. It is not the teacher's responsibility 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 make-up tests, you should take the test within one or two days after returning to class. Serious illness is the only reason for missing a test. Be on time !  It is considered( 认为)  rude to be late. Also, it disturbs 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 room. Then go to your seat and sit quietly. In the US it is not necessary to knock before you enter the classroom. If you must leave during class ,  do so quietly.  There is no need to ask the teacher's permission. Entering a teacher's office or any office with a closed door without knocking first is not acceptable.  Knock first , then wait to be invited in. Wearing a hat in class is considered impolite by many teachers. Some teachers may ignore it, but you should ask permission first. 根据短文内容，回答下列问题。 1. What should a student do if he or she doesn't understand the teacher's question? __________________________________________ 2. If a student misses a class, how can he or she find out the assignment? __________________________________________ 3. What is the only reason for missing a test? __________________________________________ 4. Is it necessary for a student to knock before he or she enters the classroom? __________________________________________ 5. Put the sentence 'Wearing a hat in class is considered impolite by many teachers. ' into Chinese. __________________________________________