Final answer:
The government is responsible for improving the collection of an existing tax by lowering the amount, increasing enforcement, and changing the method of trying violators.
Step-by-step explanation:
The answer to the question is a) The government. The government is responsible for administering and collecting taxes. In order to improve the collection of an existing tax, the government can lower the amount of the tax, increase enforcement measures, and change the method of trying violators. By implementing these strategies, the government aims to ensure that taxes are effectively collected and used to fund government operations and programs.