A good friend of mine was complaining about her son the other day．“Did you notice,” she started, “how he didn’t wait for me to get my salad before he dove into his?”
True enough, the boy attacked his plate faster than a cat in the wild．Without manners, we’re no more than animals．Actually, that’s not true．I’ve been watching and feeding a group of wild cats, and they show unusual politeness toward each other．Even when food is scarce, they take turns, leaving at least a small part for the next in line．
My mother educated her three children to have good manners all the time．We were made to feel very uncomfortable as if we were sitting on pins and needles until we got used to saying please, thank you, pardon me, and I’m sorry．And I have to say, while it was a painful learning experience, it was one of the most valuable．
I can’t tell you how often I sat with my friends, eating at their dinner tables, and their parents thought highly of my good manners．While it was a little embarrassing, I knew even then that my mother’s teachings were paying off．
Many years later, when I was attending seminars across the country, my manners were quite useful．
While I regret that I haven’t been a perfect example, I’m still working on it．I suppose, in this regard, my mother lives on through me．I didn’t have her beautiful singing voice or her green eyes, but she did make sure I received one of her finest characteristics．
小题1:What did the writer’s friend most probably complain about?
A．Her son’s eating too quickly．
B．Her son’s not having a healthy diet．
C．Her son’s not having good table manners．
D．Teenagers’ not having good manners．小题2:The underlined word “scarce” in Paragraph 3 probably means “________”．
A．too much
B．not delicious
C．not enough
D．quite hot小题3:We learn that the writer’s mother __________．
A．was strict about her children’s manners
B．never punished her children
C．had beautiful blue eyes
D．was not good at singing小题4:What does the writer think of her experience of learning good manners?
A．Easy and relaxing
B．Painful and valuable
C．Easy but useless
D．Too horrible小题5:We can infer from the passage that the writer _________．
A．is surely liked by everyone around her
B．is not satisfied with most people’s manners around her
C．thinks she has been a perfect example to the young
D．thanks her mother for teaching her the good manners a lot
，故A正确；若该微粒在运动中突然分成荷质比相同的两个粒子，则粒子所受重力与电场力的合力为零，分裂后只要速度不为零且速度方向仍与磁场方向垂直，洛伦兹力提供向心力，它们均做匀速圆周运动，故B正确；带电粒子做圆周运动，洛伦兹力提供向心力，由牛顿第二定律得：
，则轨道半径：
；如果粒子分裂后，它们的荷质比相同，而速率不同，由