The periodic function y = g(x) has a period of 6. It is known that g(1) = g(7) = 0, and that g(5) = 3 is a relative maximum of g. Which of the following must also be true A?
a. The function g must be increasing on 0 < x < 5 and decreasing on 5 < x < 7.
b. g(x)≥ 0 for all values of x.
c. g(18) ≠ g(4)
d. g(3) = g(27)