关于计算的……若2.5^x=1000,0.25^y=1000,则1/x-1/y等于（ ）A 1/3 B 3 C -1/3

由题意得：x=log2.5 1000 ,y=log0.25 1000
换底后：x=(lg1000)/(lg2.5) ,y=(lg1000)/(lg0.25)
1/x - 1/y=(lg2.5)/(lg1000) - (lg0.25)/(lg1000) =[(lg2.5)-(lg0.25)]/(lg1000)
=[lg(2.5/0.25)]/(lg1000) = (lg10)/(lg1000)=1/3
选A