缺词填空。

     School education (教育) is very important and useful. Yet no one can (1) l______ everything at school

and a teacher can't teach his students (2) e______ they want to know. His job is to (3) s______ his students

how to learn. He teaches them how to read and how to think. So the students can learn much more by

(4) t______.

     It is more (5) i______ to know how to study by oneself. It's quite easy to learn something, but it's difficult

to (6) u______ it to solve problems. Great inventors do not get everything from school, but they still can

invent many things and change the world a (7) l______ .

     How can the inventors do all of this? That's (8) b______ they know how to study. A lot of things are not

taught in the classroom. They get a lot of knowledge by reading (9) o______ school. They work hard and

never (10) g______ up all their lives.

一带电质点在匀强磁场中作圆周运动，现给定了磁场的磁感应强度，带电质点的质量和电量.若用v表示带电质点运动的速率，R表示其轨道半径，则带电质点运动的周期

A．与R有关

B．与R无关

C．与v有关

D．与v无关