“我之所以看得更远，是因为我站在巨人的肩膀上．”这虽是牛顿自_爱下问搜题

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问题填空题

“我之所以看得更远，是因为我站在巨人的肩膀上．”这虽是牛顿自谦的话，但站得高看得远却有一定的科学道理，这是因为地球表面并不是平的，而光在同种均匀介质中是沿______传播的．现代战争中为了使雷达“看”得更远，雷达装在预警机上飞上几万米的高空，雷达发出的是______（填“超声波”或“电磁波”）．若某雷达发出的波的频率是4×10⁴MHz，则其波长为______m．

答案

因为光在同种均匀介质中是沿直线传播的，而地球表面是不平的，所以我们站的高可以看得远；

雷达发出的是电磁波，如果雷达发出的波的频率是f=4×10⁴MHz，则其波长λ=

c

f

=

3×108m/s

4×1010Hz

=0.0075m；

故答案为：直线，电磁波，0.0075．

选择题

已知集合A={x|x²-3x-10≤0}，集合B={x|m+1≤x≤2m-1}，若B是A的充分条件，则实数m的取值范围是（　　）

A．[-3，3]

B．[3，+∞）

C．[0，3]

D．（-∞，3]

完形填空

When I was twelve years old. I went with my dad to his work—a car showroom. I was 21  around carelessly and saw a poor woman with a child beside her 22 outside the showroom. I saw that she was crying and went inside to tell my 23 . He went out and 24 the woman to come into the showroom. He offered her some water and then asked her what was 25 .
The woman said that her husband had died and she didn’t have anyone else in her family who could 26   her. she did some manual(体力的) labor to earn some money to 27   her daughter but she was sick for the last three days and was 28  to go to work. Now she didn’t have a grain of food to eat. While she was telling this story to my father, she was unable to   29  her emotions（情绪）and started crying again. My father and I were deeply   30  by her story.
We got some food for her and her baby. My father then took them to the nearest hospital for her baby to be 31  as she did not seem to be very well. On the way, we 32  her a 5kg-bag of wheat from the market. My father gave her some money before we left. The lady was so   33  .
It is eight years later, 34 that event is still very 35  in my mind. My father’s   36 to this woman moved me   37  and since then, I have decided to try and walk a similar path and serve others. I’m   38  to see so many other people in this world are also ready to help others when they meet people   39 . They have 40   to walk a service path also.

A．get tired of

B．take care of

D．in difficulty