问题
选择题
This book is said ________into several foreign languages last year.[ ]
A. has been translated
B. have been translated
C. to have translated
D. to have been been translated
答案
答案:D
This book is said ________into several foreign languages last year.[ ]
A. has been translated
B. have been translated
C. to have translated
D. to have been been translated
答案:D
设有关系R,S和T如下:关系T是由R和S经过什么操作得到的
R
A | B | C |
1 | 2 | 3 |
4 | 1 | 6 |
3 | 2 | 4 |
A | B | C |
4 | 1 | 6 |
2 | 7 | 1 |
A | B | C |
1 | 2 | 3 |
3 | 2 | 4 |
A.R∪S
B.R-S
C.R×S
D.R
S