设随机变量X和Y独立同分布，记U＝X－Y，V＝X＋Y，则随机变量U和V必然()
A. 不独立
B. 独立
C. 相关系数不为零
D. 相关系数为零
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What is Heaven air？ ______
A. The name of a plane.
B. The name of an airline.
C. The name of a travel agency.
D. The name of an advertising program.
The starting spot of the Changjiang River may be ______.
A. somewhere in the eastern part of China
B. somewhere in the northern part of China
C. somewhere in the place north of Tibet
D. somewhere in the place north to Tibet
Most flights of Heaven Air go to ______.
A. small towns
B. big cities
C. both big and small cities
D. the very center of Africa
听力原文：What can I do for you, Madam？
(4)
A. I don't like button and beef.
B. A bag of fruit and some vegetables, please.
C. My favorite food isn't bread and butter.
D. I don't like this meal.
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