阅读理解
Teens don't understand the big fuss (小题大做). As the first generation to grow up in a wired world,
they hardly know a time when computers weren't around, and they eagerly catch the chance to spend
hours online, chatting with friends, so what?
But researchers nationwide are increasingly worried that teens are becoming isolated, less skillful at
persontoperson relationships, and perhaps numb to the cheatings that are so much a part of the email
world."And a teen's sense of self and values may be changed in a world where personal connections can
be limitless," said Shetty Turkle.
Another researcher, Robert Kraut, said he's worried about the "opportunity costs" of so much online
time for youths.He found that teens who used computers, even just a few hours a week, showed
increased signs of loneliness and social isolation."Chatting online may be better than watching television,
but it's worse than hanging out with real friends," he said.
Today's teens, however, don't see anything strange in the fact that the computer takes up a centra
l place in their social lives."School is busy and full of pressure.There's almost no time to just hang out,"
said Parker Rice, 17."Talking online is just to catch up time."
Teens say they feel good about what they say online or taking the time to think about a reply.Some
teens admit that asking someone for a date, or breaking up, can be easier in message form, though they
don't want to do so.But they insist there's no harm.
1. The researchers argue that ________.
A. teens may develop a different sense of values
B. nothing is wrong with teens' chatting online
C. teens can manage their social connections
D. spending hours online does much good to teens
2. Teens think that talking online can help them ________.
A. use computers properly
B. improve their school work
C. develop an interest in social skills
D. reduce their mental pressures
3. The text mainly deals with ________.
A. teens' pleasant online experience
B. teens' computer skills and school work
C. the effects of the computer world on teens
D. different opinions on teens' chatting online
4. Which of the following is TRUE?
A. Teens are more skillful at persontoperson relationships.
B. Teens showed decreasing signs of loneliness and social isolation.
C. Chatting online is worse than hanging out with real friends.
D. Asking someone for a date, or breaking up, can be more difficult in message form.
5. The purpose of the text is to ________.
A. describe computer research results
B. draw attention to teens' computer habits
C. suggest ways to deal with problem teens
D. discuss problems teens have at school
的正电荷置于电场中的O点由静止释放，经过
后，电荷以v0=1．5×l04m/s的速度通过MN进入其上方的匀强磁场，磁场与纸面垂直，磁感应强度B按图b所示规律周期性变化（图b中磁场以垂直纸面向外为正，以电荷第一次通过MN时为t=0时刻）。求：
时刻电荷与第一次通过MN的位置相距多远； （3）如果电荷第一次通过MN的位置到N点的距离d=68cm，在N点上方且垂直MN放置足够大的挡板．求电荷从O点出发运动到挡板所需的时间。