Assess the following four tax policies in terms of the benefits principle versus the ability-to-pay principle.
a. A tax on gasoline that finances maintenance of state roads
b. An $8 \%$ tax on imported goods valued in excess of $\$ 800$ per household brought in on passenger flights
c. Airline-flight landing fees that pay for air traffic control
d. A reduction in the amount of income tax paid based on the number of dependent children in the household.