Chief executive is elected by the people and the executive branch is separate from the legislative branch of government

This is true. The Chief Executive is the President of the United States of America. He is known as the Chief Executive because he is the head of the Executive branch of government. The United States government was formed with the principle of separation of powers in mind. This means that government power should not be centralized in just one official or one branch (like the British monarchy in the Medieval and Renaissance era). This is done to lessen the chance for abuse in the government. The executive branch is mainly concerned with the implementation of laws. The legislative is in-charge of writing and creating the national laws. The judiciary (courts) is primarily there as a check for the powers of the executive and legislative branch. They make sure both branches do not abuse their powers and gives citizens the avenue to air out their grievances.

B) .. change at different rates to different degrees

Apart of the parietal lobe