Which best describes a role of the executive branch of the federal government?

To put it in the most basic way:
The legislative branch makes the laws (Senate and the House of Representatives).
The executive branch carries out the laws (President).
The judicial branch interprets the laws (Supreme Court).

The Executive power of the Federal Government is vested into the  President of the United States. The President acts as "Chief of State":

He is the boss of millions of governments workers who work at the agencies of the Executive Branch. He also decides the best way to enforce the laws provided by the Legislative Branch.He is entitled to hire specialists who would serve as advisors regarding certain affairs on public policy.

In 911, a group of vikings lead by rollo besieged paris and chartres. after a victory near chartres on 26 august, charles decided to negotiate with rollo. the talks were led by hervé, the archbishop of reims. this resulted in the treaty of saint-clair-sur-epte, which granted rollo and his soldiers all the land between the river epte and the sea. it also granted him brittany, "for his livelihood". at the time, brittany was an independent land which france had not been able to conquer. in exchange, rollo promised the king his loyalty and military assistance when needed. also rollo also agreed to be baptised and to marry gisela, the king's daughter. the territory given rollo is about the same as upper normandy.