For the function, find the points on the graph at which the tangent line is horizontal. If none exist, state that fact. f ( x ) = 3x - 2x + 4 Select the correct choice below and, if necessary, fill in the answer box within your choice. O A. The point(s) at which the tangent line is horizontal is (are) (Simplify your answer. Type an ordered pair. Use a comma to separate answers as needed.) B. There are no points on the graph where the tangent line is horizontal. O C. The tangent line is horizontal at all points of the graph