The correct answer to the question "The main advantage of the parliamentary form of government is that" is Option 3: the executive remains responsible to the legislature.

The parliamentary form of government is a system of democratic governance in which the executive branch (the government) is drawn from and is accountable to the legislature (parliament). In this system, the parliament has the power to elect or remove the government through a vote of no confidence, which ensures that the government remains responsible and accountable to the people`s representatives.

Option 1: "The executive and legislature work independently" is not an advantage of the parliamentary form of government but a characteristic of the presidential form of government. In a presidential system, the executive and legislature are separate and independent branches of government.

Option 2: "It provides continuity of policy and is more efficient" is also not a unique advantage of the parliamentary form of government. The effectiveness of a government`s policies depends on various factors, including the competence of the government officials, the stability of the political system, and the quality of the governance institutions.

Option 4: "The head of the government cannot be changed without election" is not a characteristic of the parliamentary system but a feature of a presidential system, where the president is elected for a fixed term and cannot be removed from office without a formal impeachment process.

The main advantage of the parliamentary form of government is that it ensures the executive remains responsible to the legislature, which means that the government must be accountable to the parliament and, by extension, to the people. This accountability ensures that the government is more responsive to the needs and aspirations of the people and is less likely to abuse its power.

Moreover, the parliamentary system allows for a more efficient decision-making process as the executive and legislature work closely together, and the government is formed from the majority party or coalition in the parliament. This allows for a quicker and more streamlined process of enacting policies and legislation.

In conclusion, the parliamentary system`s main advantage is its ability to ensure the government`s accountability to the people through its responsibility to the legislature. It also allows for a more efficient decision-making process and a streamlined governance system.