阅读短文，根据短文内容及首字母提示，在空白处填入一个适当的单词。
Ron, the teacher at the skydiving (跳伞运动) school, was surprised when the gray-haired man said that his
name was Walter and asked if he could take skydiving lessons. Ron asked him how old he was and he
(1) r that he was 60. Ron explained to Walter that (2) a over 50 had to be checked by a doctor
before he could learn to jump from a plane. "I'm sorry, but I can't let you start learning (3) w a letter
from your doctor."
Walter smiled. "Here is a letter from my doctor. He asked me to take (4) l of tests and he says that
I'm fine."
So Walter was able to join the skydiving school. He came to all the lessons and worked very (5) h .
Soon it was the time for him to make his (6) f jump. Ron asked him if he was feeling OK. Walter
answered that he had never felt better. However, he added that there was something he should have told Ron
(7) e . Ron asked what it was and Walter smiled. Then just before he jumped, he told Ron that he wasn't
60. Ron asked how old Walter (8) r was and Walter told him he was 75!
Walter has a lot of (9) h . He enjoys riding fast motorbikes and (10) c mountains. Last year
he was saved by a police helicopter (直升飞机) in Wales.
His daughter Betty worries about him. "I think he should stop all these activities. But my mother says that
as long as he's happy, it's OK."
＝2×108 C/kg的正电荷从坐标为(0,1)的A点处由静止释放．电荷所受的重力忽略不计．
m
＝2
＝10－6 s.
＝
m
＝8 m