Final answer:
Price is held constant along the demand curve. Other factors like income levels and consumer preferences that shift the demand curve are not constant when moving along the curve. Option b.
Step-by-step explanation:
The correct answer to the question of what is held constant along the demand curve is option b) Price. A demand curve is a graphical representation of the relationship between the price of a good or service and the quantity demanded for a given period of time.
When we move along the demand curve, we assume that other factors such as consumer preferences, income levels, the prices of related goods, and expectations remain unchanged.
Income levels, tastes and preferences, and other market factors affect consumer choices, but these are not held constant along the demand curve. Instead, changes in these factors shift the entire curve to the right (increase in demand) or to the left (decrease in demand).
This differs from moving along the demand curve, where the price changes but the curve itself does not shift.
So Option b.