What Was the Significance of the "Falling-Domino" Theory

What was the significance of the "falling-domino" theory?

A) The theory was a tactic of debilitating a rival country's economy by applying progressively harsh sanctions, which Eisenhower came to adopt reluctantly because the United States had become increasingly dependent on the Soviet economy.
B) Holding that the United States must be the first domino to fall by exemplifying the virtues of democratic governance, the theory was used to back Eisenhower's decision to turn away from foreign policy and focus on domestic issues at home.
C) The theory was an effective on-the-ground military strategy adopted by U.S. commanders of toppling enemy bases in quick succession, used for the first time in Vietnam and a radical departure from how the United States had fought wars in the past.
D) First used to retroactively describe how all of Southeast Asia had already fallen to Communist governments, the theory was intended to justify the Eisenhower administration's new focus on preventing communism from spreading to Europe.
E) Describing how quickly communism would spread once it infiltrated a nation, the theory was used by Eisenhower to justify beginning conflicts such as the Vietnam War, despite the fact that anti-colonial insurgencies often resulted from nationalist motives.