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问题
单项选择题
水文测站设立的（）应2～3年校测一次。
A、高程控制自校系统
B、基本水准点
C、引据水准点
D、水准点
答案
参考答案：A
解答题
选修4-4：坐标系与参数方程
直线
l：
x=a+4t
y=-1-2t
(t为参数)，圆C：ρ=2
2
cos(θ+
π
4
)
（极轴与x轴的非负半轴重合，且单位长度相同）．
（1）求圆心C到直线l的距离；
（2）若直线l被圆C截的弦长为
6
5
5
，求a
的值．
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填空题
Questions 14-18
·
Using the information in the text, complete each sentence 14-18, with a word or phrase from the list below.
·
For each sentence (14-18), mark one letter (A-G) on the Answer Sheet.
·
Do not mark any letter twice.
14. According to Dr. Score, lightning is caused by hail falling through ______.
15. The refrigerated rod served the same functions as ______.
16. Ice particles bouncing off hail falling through a cloud acquire ______.
17. In the paragraph four the word "duplicated" means ______.
18. According to S.E. Regnolds, there could be no lightning without ______.
A. copy
B. a positive charge
C. a negative charge
D. super cooled clouds
E. falling hail clouds
F. hail and super cooled clouds
G. moisture particles
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