If people believe that separation of powers is important, which of the following would not be a government they support?

The answer is : government where a single ruler, like a king, makes all the decisions.

If people believe that separation of powers is important, the option that would not be a government they support is "a government where a single ruler, like a king, makes all the decisions."
This is so because they support a democratic government with clear separation of powers like the checks and balance system of the United States, where the Executive branch, the legislative branch, and the judicial branch can't overuse their powers. They are not willing to support a king or dictator such as Adolph Hitler, Benito Mussolini, or Joseph Stalin.