问题
选择题
| Every year in April, the Water Festival ______ among the Dai people in Xishuangbanna. |
A. celebrates B. is celebrating C. is celebrated D. is being celebrated |
答案
答案：C
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| Every year in April, the Water Festival ______ among the Dai people in Xishuangbanna. |
A. celebrates B. is celebrating C. is celebrated D. is being celebrated |
答案：C
设p=(A1，A2)，(A1，A3)｝是关系R(A1，A2，A3)上的一个分解，表4-1是R上的一个关系实例r，R的函数依赖集为 (8) ，分解D (9) 。
表4-1 R上的一个关系实例r | ||
| A1 | A2 | A3 |
| a | a | d |
| a | b | e |
| a | c | f |
A．F={A1→A2,A1→A3｝
B．F={A1→A2｝
C．F={A1→A3｝
D．F={A1A3→A2,A1A2→A3｝