Total fixed costs Select one: a. are constant as output increases. b. are the costs of fixed inputs for the firm c. equal total costs minus total variable costs. d. must be paid whether the firm produces or not. e. All of these choices. Constant returns to scale occur when Select one: a. an increase in all resources causes no change in output. b. the long-run average-cost curve is declining. c. the marginal-cost curve is increasing at a decreasing rate. d. the marginal-cost curve lies below the average-cost curve. e. an increase in all resources results in an exactly proportionate increase in output. Solution Hi, Please find the answer as follows; Part A: Option E (All of these) is the correct answer. ------ Part B: Option E ( an increase in all resources results in an exactly proportionate increase in output) is the correct answer. Thanks. .