They _________ in the classroom.[ ]
A. isn't
B. aren't
C. don't
D. doesn't
答案：B
根据数据库规范化理论，下面命题中正确的是 ______。
A．若R∈2NF，则R∈3NF
B．若R∈3NF，则R不属于BCNF
C．若R∈3NF，则R∈BCNF
D．若R∈BCNF，则R∈3NF
麻疹的并发症有哪些?
