挖一条长165米的隧道，由甲、乙两个工程队从两端同时施工甲队每天向前挖6米，乙队每天向前挖5米，挖通这条隧道需要多少天？
165÷（6+5）=15（天）
鼻腔及副鼻窦恶性肿瘤的最佳治疗方式是（）。
A.单纯手术
B.单纯放疗
C.放疗结合手术
D.放疗结合化疗
E.手术结合化疗
Control valves of a CO2 system may be located within the protected space when（）.
A.it is impractical to locate them outside
B.there is also a control valve outside
C.the CO2 cylinders are also in the space
D.an automatic heat-sensing trip is installed
