Consider the production possibility frontier for a simple two-good (closed) economy. Quantities of good x produced are plotted on the horizontal axis. Quantities of good y produced are plotted on the vertical axis. Suppose that the production of both x and y depends only on labor input and that the production functions for these goods are: x = f(lx) = lx and y = f(ly) = ly. Total labor supply is limited by: lx + ly = 100. This production possibility frontier is: (HINTS: You may want to derive the production possibility frontier equation) a. convex shaped b. concave shaped c. a straight line d. Undetermined