The correct answer is:
Deciding which laws are legal and should be enforced
Explanation:
The Executive branch of the United States government is composed by the President, who is also the Commander in-Chief of the armed forces, Vice-President, Federal agencies and the Cabinet. This branch is in charge of the general administration of the country, the national security and defense, and for implementing and carrying-out the laws made by the Congress (Legislative branch) and foreign affairs.
As part of the Checks and Balance system, the President has the power to approve or veto a bill before it becomes a law, but the branch in charge of interpreting and deciding which laws are constitutional (legal) and should be enforced is the Judicial branch.