电气化铁道用避雷器的线路放电等级为（）
A.1级
B.2级
C.3级
D.4级
参考答案：A
We first met on a train in 2000. We both felt immediately that we _________ each other for years.
A．knew
B．have known
C．had known
D．know
人在呼气时，膈肌和肋间外肌的活动是[ ]
A．膈肌收缩，肋间外肌舒张
B．膈肌舒张，肋间外肌收缩
C．膈肌舒张，肋间外肌舒张
D．膈肌收缩，肋间外肌收缩
