Correct Option: D

A single-party system is a type of state in which a single political party forms the government, usually based on the existing constitution. All other parties are either outlawed or allowed to take only a limited and controlled participation in the election. Most single-party states have been ruled either by parties following the ideology of Marxism-Leninism or international solidarity, such as the Soviet Union. The People’s Republic of China is a single-party state with the Communist Party of China as the single party.