-party systems are most common in the english-speaking countries of the world? /

Two party system is the correct answer.

Explanation:

The group of people which are organised based on their political goals and political beliefs are known as political parties. They are the organisations who try to gain more votes in the elections and form governments. The main parties  in US are Democrats and Republicans and because of these two parties the US government is called as two party system. The elections are held in two stages in two party system, primary elections and general elections. The two party system is present in the most of the English speaking counties.

c or d both can be the answer