设变量x，y满足约束条件y≥xx+2y≤2x≥-2，则z=x-3y的最小值___

读图，完成下列各题．

（1）A图表示的是______半球，B图表示的是______半球．

（2）A图中的陆地面积约占______，B图中的陆地面积约占______．

（3）无论我们怎样划分，地球的任何两个大小相等的半球都是______面积大于______面积．

阅读理解。

     Shopping on the Internet is becoming more and more popular. Why do people use the Internet to shop?

Some people say it is more convenient. They don't have to leave their homes to order something; they can

shop for anything they want at any time; they can find things for sale that they can't find in the stores near

their homes. Still other people say they can find better prices on the Internet.

     If you want to buy something on the Internet, you need a credit (信用) card. You have to type your

credit card number and information on the website (网页) and send them to the store over the Internet. You

have to be sure that the store will not use your information in the wrong way. You don't want someone to

get your credit card number, so be careful with it, beause people sometimes steal (窃取) credit card numbers

from stores.

     The Internet is also a good place to go window-shopping. Window-shopping is when you look at the

things for sale in a store, but don't plan to buy anything. In window-shopping you can see what kinds of things

you are able to get and how much they cost. Some stores like Ross Stores have a website for information

about their stores, but not for shopping. Some stores have a website for information about their stores, and

can shop on-line there, such as Office Depot, Payless Shoe Source, Safeway. Some stores like Amazon. com

are only for on-line shopping.

1. Some people use the Internet to shop because ________.

A. they can sleep all day long

B. they want to leave their homes

C. they want to play with their friends

D. they can get things with less money

2. The Chinese meaning of the word "convenient" in this passage is "________".

A. 时髦的

B. 较近的

C. 方便的

D. 可用的

3. If you want to shop on the Internet, you need ________.

A. an ID card

B. a credit card

C. an IC card

D. a room card

4. Which of the following is NOT true according to the passage?

A. You can shop on-line at www.officedepot.com

B. You cannot shop on-line at www.rossstores.com

C. You can only do window-shopping at www.amazon.com

D. You can do window-shopping and shop on-line at www.safeway.com

某电视台综艺节目从接到的5000个热线电话中，抽取10名“幸运观众”，小颖打通了一次热线电话，她成为“幸运观众”的概率是______．

国产非标准设备原价的计算法有( )。

A．成本计算估价法

B．系列设备插入估价法

C．系数估算法

D．定额估价法

E．分部组合估价法

理想气体中当混合气体的总压一定时，组成气体的分压与其体积成分成何种关系？（）

A.反比

B.正比

C.二次方正比

D.三次方正比