A9. The diagram below depicts a firm's short-run production function and two isoprofit lines (and B). If the firm's optimal production point has switched from point B to point A, which of the following must have occurred? Output A. B. C. D. B A TUB Labour a decrease in the price of labour; an increase in profits an increase in the price of labour; an increase in fixed costs; no change in profits a decrease in the price of labour; a decrease in fixed costs; a decrease in profits an increase in the price of labour; an increase in profits