供给价格弹性ES=∞,此时称()。
A.供给完全无弹性
B.供给有完全弹性
C.供给为单一弹性
D.供给缺乏弹性
E.供给价格弹性无穷大
参考答案:B, E
—Could you tell us ______?
—About a month. [ ]
A. how often are they going to be there
B. how often they are going to be there
C. how long are they going to be there
D. how long they are going to be there
水溶性生物碱如何提取()
A.氯仿回流提取
B.将溶液碱化至pH值达12以上,正丁醇萃取
C.将溶液酸化至pH值达2~3,正丁醇萃取
D.将溶液碱化至pH值达12以上,雷氏铵盐沉淀
E.将溶液酸化至pH值达2~3,雷氏铵盐沉淀