Final answer:
The correct tax structures in sequence are progressive, regressive, and proportional, applying different tax rates based on income levels.
Step-by-step explanation:
A proportional tax structure applies the same tax rate to all levels of income. A progressive tax structure applies higher tax rates as the tax base increases. Lastly, a regressive tax structure applies lower tax rates as the tax base increases. Therefore, the correct sequence to fill the blanks in the question would be: A) Progressive, Regressive, Proportional.
A proportional tax structure applies the same tax rate to all levels of income, while a progressive tax structure applies higher tax rates as the tax base increases, and a regressive tax structure applies lower tax rates as the tax base increases.