Before "stand-by" is rung on the engine telegraph, it is usual to give the main engine （） ahead and astern. ["a brief trial with turning gear","a brief trial on power","a long trial by steering gear","one minutes trial with windla"]
在空间中传播时，电场和磁场两者是（），同时两者又垂直于（）。
（）主要用于扑救低沸点易燃液体，特别是大型贮油池罐可采用液下喷射泡沫灭火。 ["A.化学泡沫","B.普通蛋白泡沫","C.氟蛋白泡沫","D.抗溶性泡沫"]
Bedplates are the （） of the engine, without the support of which the shaft alignment in particular, and engine structure as a whole, would inevitably be lost. ["hull","projection","graphitization","foundatio"]
基站天馈系统包括（）、（）和天馈线的支撑、固定、连接和保护等部分。
双极化天线中两个极化波的极化方向是（）。
