Is f(x) = cos (3x) if x ≥ 0
-4 if x < 0 differentiable over the interval (-1,9) ?

A. Yes, but it would not be if the interval were (-1, 1).
B. No, but it would be if the interval were (-1, 1).
C. Yes, and it would be if the interval were (-1,1).
D. No, and it would not be if the interval were (-1, 1).