Which statement describes the rate of change of the following function?
f(x) = 9x - 4
A.
The function has a constant rate of change, decreasing for all x at a rate of 4.
B.
The function has a constant rate of change, increasing for all x at a rate of 9.
C.
The function has a varying rate of change when x > 9.
D.
The function has a varying rate of change when x < 4.