The correct answer is (C) the price of the good itself.

Explanation:

The supply curve denotes the number of goods that the producers will be willing to supply at a given price. If the movement is along the supply curve then other factors are considered to remain constant and the quantity supplied changes only due to change in own price of the commodity. This change results in either expansion or contraction of supply. Therefore, when it comes to movement along the supply curve, then the only price is not held constant.