下列属于第三代头孢菌素的抗生素是（）
A.美罗培南
B.头孢呋辛
C.噻甲酸肟头孢菌素
D.头孢西丁
E.头孢三嗪（头孢曲松钠）
参考答案：E
数据库系统的核心是______。
A．数据模型
B．数据库管理系统
C．数据库
D．数据库管理员
A certain Social Security recipient will receive an annual benefit of $12,000 provided he has annual earnings of $9,360 or less, but the benefit will be reduced by $1 for every $3 of annual earnings over $9,360. What amount of total annual earnings would result in a 50 percent reduction in the recipient’s annual Social Security benefit (Assume Social Security benefits are not counted as part of annual earnings.)（）
A.$15，360
B.$17，360
C.$18，000
D.$21，360
E.$27，360
