Final answer:
The slope of a linear demand curve is constant along the curve, but this may not apply to all types of demand curves. (option b)
Step-by-step explanation:
The slope of a linear demand curve is typically constant along the curve. This means that for a straight-line demand curve, the slope is the same at all points on the curve. A demand curve with constant unitary elasticity is concave, not straight, because the rate of price declines varies along the curve. In contrast, a curve that slopes upward with proportional increases in price and quantity represents a condition of constant elasticity. However, this does not necessarily hold for all demand curves. Specifically, a demand curve with constant unitary elasticity is not a straight line; it is concave. This is because the absolute value of price declines are not identical throughout, resulting in a slope that is steeper on the left and flatter on the right. On the other hand, when both price and quantity are increasing proportionally, the curve slopes upward, and this can be represented by a straight line with constant elasticity.
In cases where demand is inelastic, such as certain carmakers' products, costs can be passed along to consumers. Conversely, if the demand is elastic, carmakers may need to absorb these costs themselves.