The correct option to complete the statement is: A is a presidential democracy.
Belize has a parliamentary system, but it operates as a constitutional monarchy, which might lead to some confusion. However, it is most accurately described as a democracy where the Prime Minister is the head of government, rather than a presidential democracy like those found in some other countries. If the question strictly asks for how it differs from most Central American countries that typically have presidential systems, then "A" would be the closest match among the options provided.