In which political system are multiple political parties most common?

Parliamentary system

Explanation:

A parliamentary system is one in which the executive derives its power from the ability to command the confidence of the parliament. Moreover, the executive is also held accountable to that parliament. Most of the time, a parliamentary system has a head of state who is a different person than the head of government. Moreover, parliamentary systems tend to have multiple political parties represented in the legislature.

b or c im pretty sure

basic principles: federalism, separation of powers, checks and balances, judicial review, representative democracy, limited government, rule of law, individual rights and responsibilities, consent of the governed, majority rule, popular sovereignty, equal protection.