A:3x-4y-1=0
B:3x-4y-1=0或3x-4y-21=0
C:3x-4y+1=0
D:3x-4y-21=0
The price system is a complex network composed of the prices of all the products bought and sold in the economy as well as of a great number of services.
如果a、b互为倒数,x、y互为相反数,则5(x+y)﹣ab=( )