A 1 : 5 scale model of a car is tested in a wind tunnel at the same air speed that the real car will experience on the road. If the drag force on a body is proportional to the product of air density, the square of speed, and the frontal area, what is the drag-force ratio (model : prototype)?
a) 1:5
b) 1:25
c) 1:125
d) 5:1