New blackboards have been fitted up in all the classrooms.教室里都安装上了新黑板.How many blackboards are there in this room?在这个房间里有几块黑板?Some cleaned the blackboards, others mopped the floor.有些人擦黑板, 有些人拖地板....
These particulate creatures are hardly visible to the naked eyes.这些微小的生物肉眼几乎看不见。Visible particulate matter can be controlled by adequate regulations.对肉眼可见的颗粒物质的污染通过适当管理即可加以控制.Lungs retain relatively insoluble particulate...