蚊子种群数量变动是属于
A．不规则波动
B．周期性波动
C．季节消长
D．种群爆发 ( )
参考答案：C
Which of the following is used when one fails to catch what the speaker has said ( )
A．Excuse me.
B．I'm sorry.
C．Keep nodding.
D．I beg your pardon.
静脉胆囊造影观察胆管的最佳摄影时间在注药后（）
A.1～3min
B.15～30min
C.60～70min
D.90～100min
E.120～180min
