《铁路无线通信维护暂行规则》规定，接收机双工灵敏度不允许低于单工灵敏度（）。
A、3dB
B、6dB
C、7dB
D、12dB
参考答案：A
We suggest that you file a claim ______ the shipping company for all the losses incurred as a consequence of failure to ship the goods ______ Order No. 123 in time.
A．against, unless
B．for, in
C．against, in
D．against, under
支原体肺炎（）
A.常伴有头痛
B.易在冬季发生
C.常伴有咽炎，有时有大疱性鼓膜炎
D.常引起双侧肺浸润
E.治疗首选头孢菌素
