问题
选择题
This is________ pen. _________ pen is blue.[ ]
A. the, A
B. the, The
C. a, The
答案
答案：C
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This is________ pen. _________ pen is blue.[ ]
A. the, A
B. the, The
C. a, The
答案：C
若关系R和S，T如下图所示，则是执行了哪种操作才得到T
S
| B | E |
| B | 13 |
| B2 | 7 |
| B3 | 10 |
| B4 | 2 |
| B5 | 2 |
| A | B | C |
| A1 | B1 | 5 |
| A1 | B2 | 6 |
| A2 | B3 | 8 |
| A2 | B4 | 12 |
| A | R.B | C | S.B | E |
| A1 | B1 | 5 | B | 27 |
| A1 | B1 | 5 | B3 | 10 |
| A1 | B2 | 6 | B2 | 7 |
| A1 | B2 | 6 | B3 | 10 |
| A2 | B3 | 8 | B3 | 10 |
A．R
S
B．R
S
C．R
S
D．R
S
C＜E C＞E R.B＝S.B