不在纵隔内的囊肿是（）
A.食管囊肿
B.皮样囊肿
C.肺囊肿
D.支气管囊肿
E.心包囊肿
参考答案：C
A portable dry chemical fire extinguisher discharges by（）.
A.gravity when the extinguisher is turned upside down
B.pressure from a small CO2 cartridge on the extinguisher
C.air pressure from the hand pump attached to the extinguisher
D.pressure from the reaction when water is mixed with the chemical
一个完善的物流信息系统应具有哪些层次
