有三个关系R、S和T如下。由关系R和S通过运算得到关系T，则所使用的运算为（）。 A
题型：单项选择题
问题：
有三个关系R、S和T如下。
由关系R和S通过运算得到关系T，则所使用的运算为（）。
A.并
B.自然联接
C.笛卡尔积
D.交
题型：单项选择题
完成句子
1. These details________,you should pay more attention to them.(overlook)
这些细节容易被忽略,你应该对它们多加注意力.
2. ________,the gentleman took her to the party with him.(pass)
让她冒充他的女朋友,这位绅士把她带到了聚会上.
3. ________,I considered him as my best friend.(acquaintance)
认识他以后,我把他当成最好的朋友.
4. ________,an ambitious person usually works hard and has great determination.(speak)
一般来说,有雄心的人经常努力工作,并且有巨大的决心.
5. It is universally ackn
owledged that________in learning foreign languages.(superior)
众所周知,在学习外语方面女性比男性强.
6. In order to promote China's space development,Qian Xuesen________from America and made a great contribution.(hesitate)
为了促进中国太空事业的发展,钱学森毫不犹豫地从美国返回,并作出了巨大贡献.
7. Now there are many young people in our society________without hard work.(fortune)
现在我们社会中有许多年轻人梦想着不努力工作而发大财.
8. Recently he________Liu Xiang's success at the Guangzhou Asian Games.(remark)
最近,他已经对刘翔在广州亚运会上的成功作出了评论.
9. People who work in the libraries often spend a large amount of time________,therefore we are supposed to value their work.(classify)
在图书馆工作的人经常花费大量的时间为图书分类,因此我们应该珍惜他们的工作.
10. ________,he still goes on as he wishes.(condemn)
因行为不检点而受到责备,他仍然我行我素.