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【单选题】
有三个关系R、S和T如下：【图片】则由关系R和S得到关系T的操作是（ ）。A.
并
B.
投影
C.
交
D.
选择
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皮皮学刷刷变学霸
举一反三
【单选题】The doctor decided to test the chips himself because he believed that ______.
A.
nobody would dare to try it
B.
they can be used for identification purposes
C.
it has been proved successful on animals
D.
his patients expected him to experience it first
【单选题】W: Doctor Wang, would you like some coffee with cream? M: No. Personally, I like my coffee without anything. 19. How does Doctor Wang like his coffee?
A.
With cream in it.
B.
With sugar in it.
C.
With cream and sugar in it.
D.
With nothing in it.
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