Why does the writer say that it is difficult to meet the demand of the product?
Because it ______.

In a letter of refusal, you’d better make up detailed r...

判断题In a letter of refusal, you’d better make up detailed reason why you have to say no.
A、正确
B、错误

设有关系R(A,B,C) 和S(A,D,E,F)，若将关系代数表达式：∏R.A,R,R.B,S.D,S.F(R...

未知题型设有关系R(A,B,C) 和S(A,D,E,F)，若将关系代数表达式：∏R.A,R,R.B,S.D,S.F(R∞S)用SQL语言的查询语句表示，则有：SELECTR.A,B,D,F FROMR,S WHERE 【 】。

‎正常宫颈和阴道上皮中哪种细胞不常见‎A．巨噬细胞 B．T细胞 C．B细胞 D．肥大细胞

单项选择题‎正常宫颈和阴道上皮中哪种细胞不常见‎