A marine chemist issues gas free certificates and is certified by which organization? （） ["Mine Safety Appliance Association","American Chemical Society","Marine Chemists Association","National Fire Protection Associatio"]
气胀式救生筏结构主要有（）。 ①筏体 ②蓬柱 ③蓬帐 ④筏底 ⑤附属设备 ["①②③","①②③④⑤","①②③⑤"]
A major health hazard of the product tert-butylamine is that it （）. ["can be absorbed through the skin","causes irreversible damage to eye tissue","is a very unstable product","All of the above"]
A low pressure annular preventer which is used to direct flow of kick fluids away from the rig floor is called a （）. ["dump valve","deflector","separator","diverter"]
4*3复用和3*3复用相比，（）的频率复用率高，（）的干扰较小。
频率规划中4x3复用模式是指每个站（）个小区，每（）个站进行复用。
