目前主流的两种海水淡化技术是什么？
压力机的润滑系统是怎样工作的？
走访外来人口时应注意哪些礼仪？
对于灰度图像来说，颜色深度决定了该图像可以使用的亮度级别数目。
The datum from which the predicted heights of tides are reckoned in the tide tables is（）. ["mean low water","the same as that used for the charts of the locality","the highest possible level","given in table three of the tide table"]
特种通用飞机主要有哪两类？
