Travelling with Heaven Air is ______.
A. comfortable and cheap
B. expensive but pleasant
C. exciting but rare
D. quick and safe
查看答案
From this article we have learned that ______.
A. the Changjiang River is the most powerful fiver in the world
B. the Changjiang area provides a lot of food for many people in China
C. two thirds of the Changjiang River is sunny and cheerful
D. the Changjiang River is mainly a trade river
The Changjiang River is ______.
A. not only a trade river but also an agricultural river
B. just an agricultural river
C. not the widest river in the world, but it is the longest one
D. a very famous river mainly because it runs hundreds of miles
听力原文：What kind of party does the girl want to have？
(9)
A. Birthday party.
B. Graduation party.
C. Wedding ceremony.
D. New Year party.
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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