不属于焦虑分级依据的是
A.焦虑的性质
B.焦虑的强度
C.对焦虑的适应程度
D.焦虑的持续时间
E.焦虑的体征
参考答案:A
设关系R和S的元组个数分别为200和100,关系T是R与S的笛卡尔积,则T的元组个数是
A.400
B.10000
C.20000
D.90000
— does he have music lessons? —Twice a week.
A.How long
B.How far
C.How often
D.How much