13. Normal Company pays a sales commission of 4% on each unit sold. If a graph is prepared, with the vertical axis representing per-unit cost and the horizontal axis representing units sold, how would a line that depicts sales commissions be drawn? A. As a straight diagonal line, sloping upward to the right. B. As a straight diagonal line, sloping downward to the right. C. As a horizontal line. D. As a vertical line. E. As a curvilinear line