一个自动控制系统有哪些环节等组成？
参考答案：一般由输入环节、放大环节、执行环节、反馈环节及比较环节等组成。
Many things that were once considered useful and _____, for example, tobacco, is now thought harmful.
A．beneficial
B．suitable
C．fulfilling
D．accessible
我国交通法规定，24小时内累计驾车时间超过（）小时视为疲劳驾驶。
A.7
B.8
C.10
D.12
