较现代的计算机控制的三级系统指的是:一级为(),二级为过程监控级,三级为管理级。
参考答案:程序控制级,
如图所示为一轻弹簧的长度L和弹力F大小的关系,求:(1)弹簧的劲度系数为______N/m;(2)当弹力为15N时,弹簧的长度为______cm.
It is reported that very little use of these waste materials_______ in the past decades.
A.was taken
B.was made
C.has been made
D.has been taken