The correct answer is D. dictatorship.
In a dictatorship, there is only one person who rules the entire country - that person is a dictator. Famous dictators in history include Muammar Gaddafi in Libya, Saddam Hussein in Iraq, Benito Mussolini in Italy, Kim Jong-Il in Korea, etc. The other options demand a government as well as a leader, whereas a dictatorship doesn't.
