采用气压制动系统的机动车，发动机在75%的标定功率转速下，（）分钟内气压表指示气压应从零开始升至起步气压。
A.2
B.4
C.6
D.8
参考答案：B
Once air pollution in most cities, it is hard .
A．rises; dealing with
B．arouses; to be dealt with
C．raises; dealt with
D．arises; to deal with
若k＞0，点P（-k，k）在第_____象限（ ）
A．第一象限
B．第二象限
C．第三象限
D．第四象限
