将一个未知电阻和一个阻值为R₀的已知电阻串联，接在电压为U的电源两端．用电流表测量电路中通过的电流为I，通电时间为t，则未知电阻消耗的电能为____ ．

How to write an email?

    While many people are accessible by email, sometimes it is difficult to determine how exactly to write an email to them. Here are some tips for you to follow.

Write an appropriate subject line. The subject line should tell the recipient (接收者) immediately what the email is about. ____Remember that your wording also has to be brief.

    ____ It is best to be more formal rather than informal, so when writing to someone you have never met or written to before, a “Dear Jane Smith” is appropriate. When addressing someone whom you are a little familiar with, a “Dr. Smith” is okay until they tell you to address them by their first name, in which case a simple “Jane” will be okay.

    ____ Within the first two sentences of your email, your recipient should know exactly why you are writing to him. Sometimes an introduction may have to precede (先于) the sentence that states why you are writing, and sometimes it has to follow.

    Use appropriate language. You may be used to using informal language in certain social settings. ____Even when dealing with colleagues or friends you are familiar with, do not immediately fall back on informal language.

    Keep it simple. People may get dozens and even hundreds of emails a day.____In that way, they can save much of their time when reading emails.

A. Use proper greetings.

B. Express your ideas clearly.

C. State your purpose at the beginning.

D. Be as specific as possible when writing the subject.

E. However, an email may not be the best place to use such language.

F. It is important to check the language to avoid spelling and grammar mistakes.

G. It is always easier for them if you keep your email as short and brief as possible.

深：①颜色浓；②距离开始的时间很久；③深奥；④从表面到底的距离大。

A河水很深。____

B这件衣服颜色太深了。____

C夜深了，爸爸还在加班。____

D这道题太深了，小兰不会做。____

阅读下列短文，根据短文内容，从短文后各题所给的A、B、C、 D四个选项中，选择最佳选项。

How to Be a Better Student

    Maybe you are a common student. You probably think you will never be a top student. This is not necessary so, however. Anyone can become a better student if he or she wants to. Here's how:

Plan your time carefully. When you plan your week, you should make a list of things that you have to do. After making this list, you should make a schedule of your time. First set your time for eating, sleeping, dressing, etc. Then decide a good, regular time for studying. Don't forget to set aside enough time for entertainment. A weekly schedule may not solve all your problems, but it will force you to realize what is happening to your time.

    Find a good place to study. Look around the house for a good study area. Keep this space, which may be a desk or simply a corner of your room, free of everything but study materials. No games, radios, or television! When you sit down to study, concentrate on the subject.

    Make good use of your time in class. Take advantage of class time to listen to everything the teachers say. Really listening in class means less work later. Taking notes will help you remember what the teacher says.

    Study regularly. When you get home from school, go over your notes, review the important points that your teacher is going to discuss the next day, read that material. This will help you understand the next class. If you do these things regularly, the material will become more meaningful, and you will remember it longer.

    Develop a good attitude about tests. The purpose of a test is to show what you have learned about a subject. They help you remember your new knowledge. The world won't end if you don't pass a test, so don't be over worried.

    There are other methods that might help you with your studying. You will probably discover them after you have tried these.