在某一时刻突然作用到系统上并且保持在整个幅度的干扰是（）。
A、阶跃干扰
B、脉冲干扰
C、斜坡干扰
D、抛物线干扰
参考答案：A
—The rain ________ fast and heavy.
—You should ________ some shelter. Look at you—you are all wet.
A．is coming; find
B．comes; have found
C．came; find
D．came; have found
什么叫指示压力？
