低压供电系统中，当保护线(PE线)与相线所用材质相同时，且相线截面大于16mm2，小

设a∈R，函数f（x）=x³+ax²+（a-3）x的导函数是f′（x），若f′（x）是偶函数，则以下结论正确的是[ ]

A．y=f（x）的极大值为-2

B．y=f（x）的极大值为2

C．y=f（x）的极小值为-1

D．y= f（x）的极小值为1

对于居住区绿地率，新区建设需达到()，旧区改造()。

A．35%；30%

B．不应低于35%；不宜低于30%

C．30%；25%

D．不应低于30%；不宜低于25%

在车削螺纹工艺中检查螺纹中径较精确的方法是（）.

A.螺纹千分尺法

B.罗纹环规法

C.三针测量法

阅读理解。

    I have a rule for travel: never carry a map. I prefer to ask for directions (方向).

    Foreign visitors are often puzzled in Japan because most streets there don't have names. In Japan, people

use landmarks in their directions instead of street names. For example, the Japanese will say to travelers,

"Go straight down to the corner. Turn left at the big hotel and go past a fruit market. The post office is across

from the bus stop." 

    In the countryside of the American Midwest, usually there are not many landmarks. There are no mountains,

so the land is very flat (平坦的). In many places there are no towns or buildings within miles. Instead of

landmarks, people will tell you directions and distance. In Kansas or Iowa, for example, people will say, "Go

north two miles. Turn east, and then go another mile."

    People in Los Angeles, California, have no idea of distance on the map: they measure (测量) distance by

means of time, not miles. "How far away is the post office?" you ask. "Oh," they answer, "It's about five

minutes from here." You say, "Yes, but how many miles away is it?" They don't know.

    People in Greece sometimes do not even try to give directions because visitors seldom (很少) understand

the Greek language. Instead of giving you the direction, a Greek will often say, "Follow me." Then he will lead

you through the streets of the city to the post office.

    Sometimes a person doesn't know the answer to your question. What happens in this situation? A New

Yorker might say, "sorry, I have no idea." But in Yucatan, Mexico, no one answers, "I don't know." People in

Yucatan think that "I don't know" is impolite. They usually give an answer, often a wrong one. A visitor can

get very, very lost in Yucatan!

    One thing will help you everywhere ---- in Japan, in the United States, in Greece, in Mexico, or in any other

place. You might not understand a person's words, but maybe you can understand his body language. He or

she will usually turn and then point in the correct direction. Go in that direction and you may find the post

office!

1. The passage mainly tells that _____. [ ]

A. never carry a map for travel

B. there are not many landmarks in the American Midwest

C. there are different ways to give directions in different parts of the world

D. New Yorkers often say, "I have no idea," but people in Yucatan, Mexico, never say this

2. The passage says, "In Japan, people use landmarks in their directions." The word "landmark" means _____. [ ]

A. building names

B. street names

C. hotels, marks and bus stops

D. buildings or places which are easily recognized

3. In which place do people tell distance by means of time? [ ]

A. Japan

B. American Midwest

C. Los Angles, California

D. Greece

4. In the passage, _____ countries are mentioned (提到) by the writer. [ ]

A. seven

B. four

C. eight

D. five

5. Which of the following is wrong? [ ]

A. Travelers can learn about people's customs by asking questions about directions.

B. A person's body language can help you understand directions.

C. People in some places give directions in miles, but people in other places give directions by means of time.

D. People in different places always give directions in the same way.

轻烃回收装置既提高经济效益，又改善了环境。