The manufacturer of a new product developed the following expression to predict the monthly profit, in thousands of dollars, from sales of the product when it is sold at a unit price of x dollars. What is represented by the zero(s) of the expression? A. the unit price(s) when profit is greatest B. the profit when the unit price is greatest C. the profit when the unit price is equal to 0 D. the unit price(s) when the profit is equal to 0