Which of the following demonstrates the law of supply?

a. When the price of leather belts rose, leather belt sellers increase their quantity supplied of leather belts.

b. When car production technology improved, car producers increased their supply of cars.

c. When sweater producers expected sweater prices to rise in the near future, they decreased their current supply of sweaters.

d. When ketchup prices rose, ketchup sellers decreased their quantity supplied of ketchup.

a. When price of leather belts rose, the leather belt sellers increase their quantity supplied of leather belts.

Explanation:

Law of supply: The increase in price of goods increases the quantity supplied of the same good, keeping all other factors constant.

This means if the price of good increases, the producers tend to produce more of such goods. Thus, the quantity supplied in the market for such good also increases.

Here,

The price of leather belt increased which convinced the producers of leather belts to increase the level of production. This increased the quantity supplied of leather belts in the market.