问题 单项选择题

如图所示,杆件横截面面积为A,杆中最大正应力为()。

A.A

B.B

C.C

D.D

答案

参考答案:C

解析:

轴向拉压杆正应力公式中,N是内力。本题内力中最大轴力为Nmax=5F-2F=3F。这种类型的题在扭转杆中也常出现。易犯的错误是把最大外力5F代入公式。故选(C)。

单项选择题
阅读理解

阅读理解。

     The United States government has started a website to help children think critically about the advertising

that is aimed at them. The new site is called Admongo. It claims to provide visitors with an "aducation"

through games and other entertainment.

     A cartoon man dressed in old time pilot clothing greets visitors to Admongo. "Call me Haiz" he says upon

arrival in a rocket ship that opens up with a crazy world inside it. Dabce plays in the background as Haiz tells

visitors that they need to learn about advertising.

     The Admongo website is aimed at children eight to twelve years old. Its inventors say that is the age kids

develop their critical thinking abilities. Kids that age are also a big market for advertisers.

     The idea behind Admongo is to teach children three things: to identify the advertiser, to know what the

advertiser is really saying, and to know what the advertisement is trying to get the child to do.

     Children learn these things through a video game. They create their own game character. They can choose

different skin colors, hairstyles, eye and mouth shapes. Then they begin a trip through ad- land. They take a

walk through the neighborhood. They seek out the advertising and capture treasures. There are ads on buses

and billboards. The players have to find all the marketing in the neighborhood before they can move on to the

next level.

     The Admongo game takes players inside a home, to the advertising studio and everywhere else ads can be

found. It is a complete exploration of the world of marketing.

     One such area is food marketing. The Federal Trade Commission says it is an especially big business. The

F. T. C. estimates that food, drink and fast-food restaurants spent more that one and a half billion dollars on

advertising to young people in 2009.

     The F. T. C. says children are important for three reasons. They buy products. They influence parents and

caregivers to buy. And they are the future adult buyers of the products.

     A recent study says most advertising aimed at children is for foods of the lowest nutritional value. First

Lady Michelle Obama has said she would like to see advertisers marketing healthy foods for children.

1. What is the best title of the text?

A. A website aimed at children's food

B. The cartoon guide named "Haiz"

C. An"aducation" website for children

D. A popular online video game

2. Why did the government start the website?

A. To advertise the video game for children.

B. To help children know about advertising.

C. To attract the biggest market of buyers.

D. To sell the products of its company.

3. What can players do in the website game?

A. They can play video games in the trip.

B. They can travel to a supermarket.

C. They can choose hairstyles for their own character. 

D. They can eat in a fast-food restaurant.

4. Children are important for advertising because they ____.

A. are the most important for society

B. are the most potential buyers

C. are easily influenced by ads 

D. are easily affected by low-quality products

5. According to Michelle Obama, lots of foods advertised for children are ________.

A. of low quality

B. yummy

C. of high nutrition

D. healthy