问题 选择题

如图是一辆汽车做直线运动的位移时间x-t图象,对线段OA、AB、BC、CD所表示的运动,下列说法正确的是(  )

A.OA段运动最快

B.AB段物体做匀速直线运动

C.CD段表示的运动方向与初始运动方向相反

D.4h内,汽车的位移大小为30km

答案

A、由图得知:CD段斜率最大,速度最大,物体运动最快.故A错误.

    B、AB段物体位移不随时间变化,处于静止状态.故B错误.

    C、CD段斜率为负值,速度为负值,表示物体的运动方向与初始运动方向相反.故C正确.

    D、4h内,汽车的位移大小为0.故D错误.

故选C

填空题
阅读理解

阅读理解

                                                                     Stop Spam!

     When I first got an email account ten years ago, I received communications only from family, friends,

and colleagues.Now it seems that every time I check my email, I have an endless series of advertisements and other correspondence that do not interest me at all.If we want email to continue to be useful,we need

specific laws that make spamming(发送垃圾邮件) a crime.

    If lawmakers do not do something soon to prohibit spam, the problem will certainly get much worse.

Computer programs allow spammers to send hundreds of millions of emails  almost instantly.As more

and more advertisers turn to spam to sell their products, individual (个人的) email boxes are often

flooded with spam emails.Would people continue to use email if they had to deal with an annoying amount of spam each time?

    This problem is troubling for individuals and companies as well.Many spam emails contain computer

viruses that can shut down the entire network of a company.Companies rely on email for their employees

to communicate with each other.Spam frequently causes failures in their local communications networks,

and their employees are thus unable to communicate effectively.Such a situation results in a loss of

productivity and requires companies to repeatedly repair their networks.These computer problems raise

production costs of companies, which are, in the end, passed on to the consumer.

    For these reasons,I believe that lawmakers need to legislate(立法) against spam.Spammers should be

fined,and perhaps sent to prison if they continue to disturb people.Email is a tool which helps people all

over the world to communicate conveniently, but spam is destroying this convenience.

1. What does the underlined word"correspondence"in Paragraph 1 probably mean?

A. messages              

B. ideas

C. connections            

D. programs

2. According to the text, what is the major cause of the flooding spam?

A. Companies rely on email for communications.

B. More people in the world communicate by email.

C. Many computer viruses contain spam emails.

D. More advertisers begin to promote sales through spam.

3. According to Paragraph 3, who is the final victim of spam?

A. The business.       

B. The advertiser.

C. The employee.      

D. The consumer.

4. What is the purpose of the text?

A. To inform.          

B. To educate.

C. To persuade.          

D. To instruct.