已知一组样本数据a,4,2,5,3的平均数是4,方差是_________.
2
Tom feared to go home after his failure in the exam because the ____ stream of discontent from his
parents would drive him crazy. [ ]
A. actual
B. gradual
C. efficient
D. constant
数控车床的运动量是由数控系统内的可编程控制器PLC控制的。