从控制功能上分，PIS系统可分为（）个层次。 ["4","3","2","1"]
根据GB2811-2007《安全帽》4.1.7中规定，普通安全帽的质量不超过（） ["400g","430g","600g","630g"]
新核心系统中交易代码为（）位。 ["5","6","7","8"]
An ABC dry chemical fire extinguisher would be least effective against a fire in（）. ["a mattress","spilled liquids such as oil or paint","high voltage electrical gear","a trash ca"]
对仪器高正确的说法是（）。 ["测站点到经纬仪横轴中心的铅垂距离","测站点到水准仪望远镜视准轴的垂直距离","架头到经纬仪水平度盘中心的垂直距离","架头到水准仪物镜光学中心中心的距离","三角架的高度"]
管道内的流体速度，在什么位置最大？在什么位置等于零？
