42 The cost of factory machinery purchased last year is: A. A.an opportunity cost. A. B. B.a differential cost. C. B. C.a direct materials cost. C. D. a sunk cost. QUESTION 43 In describing the cost equation, Y = a + bX, "a" is: A. the dependent variable cost. B. the independent variable the level of activity. C. the total fixed cost. D. the variable cost per unit of activity