阅读理解。
Dear Amy,
Is there any way I can get my mum to drive to school? She says walking is good exercise. My friend
Ann lives closer to the school, but her mum drives her to school. She is there in two or three minutes! Going
by car is the fastest way. She doesn't get wet if it is mining either. It takes me about ten minutes to walk to
school. If it rains, I'll get wet. It isn't fair} What shall I do?
Mary
Dear Mary,
I think you want me to feel sorry for you! But I don't feel sorry for you. I think you just want a few
more minutes in bed in the morning. Walking is good exercise! Lots of people don't get enough exercise,
so I think it is probably a good, idea for you to walk. You are going to school in the healthiest way. You
may not be the closest to the school, but you are close. A ten-minute walk to school each day will help to
keep you fit. Maybe you need an umbrella for wet days? I'm sure your mother has made sure you have a
good coat and. boots (雨靴) for wet days. Maybe you just don't want to use them because they are not in?
Try to think positively (积极地) about the walk!
Amy
1. In the first letter, Mary _________.
A. gives warnings
B. gives advice
C. asks for advice
D. expresses thanks
2. What will probably happen to Mary on wet days?
A. She'll get wet.
B. She'll go to school in her mother's car.
C. She'll get sick.
D. She'll drive to school.
3. How long does it take Mary to school?
A. 2 or 3 minutes' walk.
B. 10 minutes' walk.
C. 2 or 3 minutes' drive.
D. 10 minutes' drive
4. What does Amy tell Mary to do?
A. Have a talk with her mother.
B. Do a lot of exercise instead of walking every day.
C. Ask Ann and her mother for help.
D. Take the way of walking to school as it is good exercise.
5. What does "in" mean?
A. New.
B. Fashionable.
C. Tidy.
D. Traditional.
点向
点运动
，圆周运动的半径
，洛仑兹力不做功，粒子的速率不变，偏转半径变小，说明B变强，根据曲线运动的特点，合外力指向弧内，则洛伦兹力指向右侧，根据左手定则及右手螺旋定则可以判断，M中通有自上而下的恒定电流，带负电的粒子从
点向
点运动，故A正确。