管路由直径为57×3.5mm的细管,逐渐扩大到108×4mm的粗管,若流体在细管内的流速为4m/s。则在粗管内的流速为_______。( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
免费的网站请分享给朋友吧