A toll bridge charges $0.60 for all vehicles with two axles, $1.20 for all vehicles with three axles, $1.80 for all vehicles with four axles, and $2.40 for all vehicles with five or more axles. The total revenue collected in one day is represented by the expression below. $0.60a + $1.20b + $1.80c + $2.40d

What is the best interpretation of b in the expression above?
A.
The total revenue collected from vehicles with two axles.

B.
The total number of vehicles with three axles that paid the toll.

C.
The total revenue collected from vehicles with three axles.

D.
The total number of vehicles with two axles that paid the toll.