下列哪种药物有4个旋光异构体,而只有1R,2R-D(-)异构体有抗菌活性()
A.青霉素V
B.阿奇霉素
C.氯霉素
D.红霉素
E.罗红霉素
参考答案:C
简述前陆盆地的构造变形特征。
The rich man gave away 5 _____ his money to charity to help the poor children in Africa.
A.millions
B.million
C.millions of
D.million of