1. The sales, S, of a product in units sold is given by the function S = f(p,a), where p is the price of the product (in dollars per unit) and a is the amount spent on advertising (in thousands of dollars). In interpreting the statement, fp(8,12)=-120, which of the following statements below should be used in giving a full interpretation of the meaning of this statement? I) If $12,000 is spent on advertising and at a price of $8 per unit... II) sales will decrease by about 120 units if the price per unit is raised by $1 and... III) sales will decrease by about 120 units if $1,000 more is spent in advertising and... IV) the price per unit is maintained at $8. V) the amount spent on advertising is maintained at $12,000. B) I, III, IV C) I, III, V D) I, II, IV A) I, II, V E) All of them