“x的3倍与y的差”用代数式可以表示为（ ）．
3x﹣y
离心泵的特性曲线对泵的操作运行有什么指导意义？
After knocking down the old man, the inhuman driver left the accident scene in a
hurry, the law to punish him.
A．defeating
B．challenging
C．informing
D．absorbing
