Parliamentary and presidential governments can be distinguished mainly by the legislative-executive relations. In a parliamentary government, the legislative and executive branches are closely intertwined. The executive branch, headed by the Prime Minister, is formed by the majority party or coalition in the parliament. The Prime Minister and the cabinet are accountable to the parliament, and the parliament can vote no-confidence to remove the Prime Minister from office. The legislative and executive powers are concentrated in the hands of the parliament.

In contrast, in a presidential government, the legislative and executive branches are separate and independent. The president is elected separately from the legislature and has the powers to make decisions and implement policies without the direct involvement of the legislature. The legislative and executive powers are divided, and the president is not accountable to the legislature in the same way as in a parliamentary system.

Therefore, the correct answer is 4) the legislative-executive relations.