国际贸易按商品流向划分，可分为（） A.出口贸易 B.进口贸易 C.转口贸易 D.过

在数列{a_n}中，“an=cqn(q≠0且c∈R）”是“{a_n}是等比数列”的（　　）

A．充分不必要条件

B．必要不充分条件

C．充要条件

D．既不充分也不必要条件

阅读理解。

     A smile will tell people around you that you are a kind and friendly person. However, many people

 don't smile because they think they have ugly teeth. For example, one of my classmates, Mike, doesn't

 have very nice teeth, so that is why he seldom opens his mouth. He even says that he has lost confidence

 because of his teeth. So it is very important for us to look after our teeth. In fact, a lot of people have this problem. Some people inherit teeth problems from their parents, while others' teeth are damaged because

  of bad habits, like heavy smoking, eating too much sugar or not brushing teeth often. If your teeth are in

 bad shape, you should see a dentist and ask for help. They can help improve your teeth and tell you how

 to take care of them.

     Smiling can help you to feel more confident and make other people think of you as a more friendly

 person. If' you want to keep healthy, you should not only smile but also laugh. An Indian doctor called

 Kataria said that young children should laugh about 300 times a day, while adults should laugh between 7

  and 15 times a day. So please take this chance to smile and laugh now!

1. What has made Mike lose his confidence?

    A. His bad habit.

    B. His bad teeth.

    C. Not smiling.

    D. Eating too much sugar.

2. Many people don't smile because _____.  

    A. they don't like smiling

    B. they think they are ugly

    C. their teeth are not beautiful

    D. they can't open their mouths

3. What can a dentist do according to the passage?

    A. A dentist can help improve your bad teeth.

    B. A dentist can tell you how to take care of your bad teeth.

    C. A dentist can tell you how to brush your teeth.

    D. Both A and B．

4. If you want to keep healthy, you had better _____.

    A. not smile often

    B. laugh all the time

    C. neither smile nor laugh

    D. smile and even laugh often

5. How many times should a child laugh every day in doctor Kataria's opinion?

    A. Either 300 or 30 times a day.

    B. Between 7 and 15 times a day.

    C. About 300 times a day.

    D. Only 30 times a day.

关于全口义齿颌间距离过小时的后牙排列表述正确的是（）

A.只能选用塑料牙

B.只能选用非解剖式牙

C.注意平分间距离

D.磨改盖嵴面，降低牙冠高度

E.不必排成正常的颌曲线

下列属于条件反射的是（）

A.咀嚼、吞咽食物引起胃液分泌

B.闻到食物香味引起唾液分泌

C.叩击股四头肌肌腱引起小腿前伸

D.异物接触角膜引起眼睑闭合

E.强光刺激视网膜引起瞳孔缩小

简述双重呼吸的过程（飞行时）。