Questions 18 to 20 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions. Now listen to the passage.
A. What is the percentage of Americans aging six and older who play computer and video games
B. A. 15. R 50. C. 8. D. 39.
结构中含有五个手性碳原子的为( )。
A. 盐酸吗啡
B. 盐酸哌替啶
C. 右丙氧芬
D. 盐酸布桂嗪
E. 盐酸溴己新
( )为合成类抗结核药。
A. 盐酸环丙沙星
B. 氧氟沙星
C. 利福平
D. 盐酸乙胺丁醇
( )为结构中含有4-甲基-1-哌嗪基的喹诺酮类药物。
A. 盐酸环丙沙星
B. 氧氟沙星
C. 利福平
D. 盐酸乙胺丁醇