The two principles of taxation are the benefit principle and the ability-to-pay principle.

Benefit principle - concept of taxation in public finance. It is said that whoever benefits more from public or government expenditure should pay more taxes to support the expenditure.

Ability-to-pay principle - progressive taxation wherein people earning more are subject to bigger taxes because they have the ability to pay more. Taxes should be levied according to the individual's ability to pay. 

The answer is a. i think