Figure 26-1 Production Function Output per worker on the vertical axis. Capital per worker on the horizontal axis. A concave production function starts at the origin. The curve increases capital but becomes flatter as the amount of capital increases. Refer to Figure 26-1. The curve becomes flatter as the amount of capital per worker increases because of a. diminishing returns to labor. b. increasing returns to labor. c. increasing returns to capital. d. diminishing returns to capital