Answer: A. regulating trade between states
Regulation of trade is done exclusively by the states. To ensure a free, fair, and competitive economy, the need to regulate trade is of utmost importance. Imposing tariffs, import quotas, and licenses, are ways in which trade can be regulated in a particular jurisdiction. The state government has the authority to regulate intrastate commerce and this is very important as it helps in protecting local markets from foreign competition. Trade is also regulated to earn more revenue for the state. Although trade regulation can reduce the efficiency of the economy, it is still practiced all over the world.