While the World War I started in 1914, the United States was vehemently focused on remaining neutral - At the time it was not prepared for a major military action and did not have any direct involvement with the situation - until it decided to join the conflict in 1917.
The change in course by President Woodrow Wilson was mainly caused by their links to Britain, Teuton propaganda, and the sinking of ships by German boats, among other incidents, and it showcased how the country's decision to join the struggle was not driven by an isolationist posture, but more of a lack of preparation.
Even as time has passed and the military power of the US have grown exponentially since WWI, time and time again have proven that, while the country's forces may be among the top in the planet, it will never reach a point in which they will be considered the sole power of the world.
Therefore, the answer is option A: "To emphasize that the United States was never completely isolationist nor will it ever be all powerful."