Final answer:
The correct statement that applies to both presidential and parliamentary democracies is 'The head of government is separate from the head of state,' yet this is primarily associated with presidential systems.
Step-by-step explanation:
The question you have posed pertains to the commonalities between presidential and parliamentary democracies. Evaluating the options provided, the correct answer is that 'The head of government is separate from the head of state' applies to both presidential and parliamentary systems. However, this statement is generally more reflective of presidential systems where these roles are clearly distinct. In parliamentary systems, the distinction may vary, particularly in constitutional monarchies where the monarch is the head of state while the prime minister is the head of government but may be seen as intertwining the roles of head of state and government in some cases.
In presidential democracies, like the United States, the president is both the head of state and government, and their power is independent of the legislative branch. Conversely, in parliamentary democracies, the head of government (the prime minister) is typically separate from the ceremonial or constitutional head of state such as a monarch or president and is chosen by the legislature. Semi-presidential systems incorporate elements of both, with a popularly elected president and a prime minister who depends on the confidence of the legislature.