问题 不定项选择

如图所示,a、b、c、d是某匀强电场中的四个点,它们正好是一个矩形的四个顶点ab=cd=L,ad=bc=2L,电场线与矩形所在平面平行。已知a、b、d点的电势分别为20V,24V和12V,一个质子以速度v0经过b点,速度方向与bc成45°角,经过一段时间质子经过c点,不计质子的重力,则:

[ ]

A.c点的电势低于a点电势

B.场强方向由b指向d

C.质子从b点运动到c点,电场力做功8eV

D.质子从b点运动到c点,电场力做功10eV

答案

AC

选择题
阅读理解

阅读理解。

     "Children should not be left unsupervised (无人监督的) to play with a dog." say experts in this

week's British Medical Journal. Their advice is part of a review aimed at doctors who deal with dog bites.

     "Dog bites and maulings are a worldwide problem, particularly in children." write Marina Morgan and

John Palmer. Every year 250,000 people who have been bitten by dogs attend minor injuries and

emergency units in the United Kingdom, and half of all children are reportedly bitten by dogs at some

time, boys more than girls.

     Accurate death figures are difficult to obtain, but in the past five years, two to three cases a year have

made news headlines.

     Based on the latest medical evidence, they advise doctors how to examine and treat a patient

presenting with a dog bite. They discuss the risk of infection and when to refer to specialist care. For

travelers bitten abroad, they suggest assessing the risk of rabies(狂犬病).

     In terms of prevention, they suggest that children should be taught to treat dogs with respect, avoid

direct eye contact, and not tease them. They should be taught not to approach an unfamiliar dog; play

with any dog unless under close supervision; run or scream in the presence of a dog; pet a dog without

first letting it sniff you; or disturb a dog that is eating, sleeping, or caring for its babies.

     "Dog owners also need to change their behavior", says Rachel Besser, a children's doctor and lifetime

dog owner, in an article.

     "It is clear that not all dog owners appreciate that children should not be left unsupervised with a dog",

she says. Just as some parents are obliged to take parenting classes, she would like to see compulsive

classes for expectant dog owners to teach them about the responsibilities of dog ownership. Educational

programs are also needed to teach children about some precautionary (预防的) behaviors around dogs.

      Finally, she would like to see animal doctors advising dog owners about bite prevention, and doctors

promoting bite prevention when treating patients who have been bitten by dogs.     

1. Dog biting is a problem which _____.  

A. should be paid attention to              

B. only happens to a few children

C. only boys may meet with              

D. has made news headlines

2. The underlined word "they" in Paragraph 4 refers to "________" .

A. doctors        

B. parents            

C. experts            

D dog owners

3. To avoid dog bites, a child should be taught to_____.

A. have direct eye contact

B. approach an unfamiliar dog

C. run or scream in the presence of a dog

D. leave a dog feeding itself

4. What are Rachel Besser's words mainly about?

A. It's necessary to teach children how to raise dogs.

B. Children should be taught not to play with dogs.

C. Some dog owners would like children to be left unsupervised with a dog.

D. All the dog owners would like to attend classes on caring for dogs.  

5. Which of the following can be the best title for the passage?

A. Dogs, Dangerous To Children

B. Children Should Know Behaviors Around Dogs

C. Doctors, Treat Dog Bites Correctly

D. Never Leave Children Unsupervised With Dogs