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