应急救援预案按行政区域可划分为()级。
A、三级
B、四级
C、五级
参考答案:C
In order to keep the balance of ecosystem, every possible means _______to deal with the problems of the over-exploiting of natural resources.
A.has tried
B.has been tried
C.have taken
D.have been taken
开车时透平推力的变化是()。
A.向后转向前
B.向前转向后
C.全部向前
D.全部向后