The periodic function y = g(z) 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. The function g must be increasing on 0B. g(z)≥0 for all values of 2.
C. g(18) ≠ g(4)
D. g(3) = g(27)
