治疗伤寒的首选药物是（）
A.氨苄青霉素
B.复方新诺明
C.氟喹诺酮类
D.痢特灵
E.黄连素
参考答案：C
随着生态演替的发展，正相互作用增加负相互作用减少。
In order to make students have a good knowledge of science subjects, they are encouraged to______ their own science experiments.
A．operate
B．direct
C．manage
D．conduct
