Which of the Following Statements Is True

Multiple Choice

Which of the following statements is true?

A) If marginal costs are constant, then it is optimal to advertise until the last dollar spent on advertising generates one additional dollar of sales.
B) If the demand curve shifts leftward as the advertising expenditure increases, then the advertising elasticity of demand is positive.
C) If the advertising elasticity of demand declines and consumer demand becomes more price elastic, then the optimal advertising-to-sales ratio declines.
D) If the advertising elasticity of demand is positive, then the demand curve must be upward sloping.