The pattern is min-zero-max-zero-min, which is the pattern for a cosine function of the form y = acos(x) + k, but is reflected over the x-axis (so a < 0).
B
The amplitude is |a|, so a = –1 and |a| = 1.
C
The midline is exactly between the max and the min, y = (6 + 8)/2 = 7, so k = 7.