下列计算结果正确的是 [ ]
A.2x+5y=7xy
B.2a2+2a3=4a5
C.4a2﹣3a2=1
D.﹣2a2b+a2b=﹣a2b
答案:D
Before hydraulic starting of an engine on a covered lifeboat,what need NOT be checked?()
A.Fuel supply line valve
B.Pressure registered on the accumulator gauge
C.Cold-spark voltage readings test lamp
D.Engine stop control
海关在进口环节征收的增值税、消费税附加征收城建税。