题目内容
（请给出正确答案）
[主观题]
She didn't know______to express her ideas in English clearly in public.A．whichB．whyC．whatD
She didn't know______to express her ideas in English clearly in public.
A．which
B．why
C．what
D．how
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当关系模式R(A，B) 已属于3NF，下列说法中哪一个是正确的？
A．它一定消除了插入和删除异常
B．仍存在一定的插入和删除异常
C．一定属于BCNF
D．A)和C)都是
