关系数据库管理系统能实现的专门关系运算包括选择、连接和 【5】 。
参考答案:投影
解析: 关系数据库管理系统的专门关系运算包括选择、连接和投影。
词汇运用 。
1. Would you mind _________(close) the door?
2. The weather will become _________(bad) than before.
3. They didn’t know how _________(go) there..
4. I am _________(excite) to hear the real story
5. I don’t know the _________(important) of learning English.
6.The twins looked at each other with a smile.They decided to keep their secret to_________(they).
7. Please don’t go out. It’s raining_________(heavy).
8. It’s _________(possible) for him to go out because he likes reading at home.
9.The elephants walked a long way. Let them stop__________(have) a rest.
10. He is driving fast along the road in the __________(direct) of Nanjing.
关于恐缩症的说法错误的是()
A.恐缩症的发生与当地人群的文化信念有关
B.恐缩症可以集体或散在发生
C.精神症状常常是一种恐怖性焦急的发作
D.多数患者每天发作2~8次
E.恐缩症预后良好