If f(x) is a decreasing function, which of the following statements must be true? Select all that apply.

(Assume that f(x) is always decreasing.)

a) f(5)−f(1) / 5−1 > 0
b) f(5)−f(1) / 5−1 < 0
c) For some value of x≠5, f(x)=f(5)
d) f(5) < f(1)
e) f(5) > f(1)