The correct answers to this question are that the United States and France had been allies for more than 150 years; and if Vietnam fell to Communism, its neighbors, Laos and Cambodia, might fall too.
The Vietnam War and all the previous revolutionary process (which includes the war between Vietnam and France) must be understood as part of the Cold War, which confronted communism and capitalism.
France was, together with Great Britain, the main ideological ally of the United States on the capitalist side. On the other hand, the relations with France had been of collaboration from the same War of Independence of the United States (with some exceptions, like the Quasi-War). The United States had been the main collaborator of France in the Second World War, which was an event that had strengthened this relationship between both countries.
In addition, the Cold War posed the threat of communism. This had spread in Eastern Europe and Asia, thanks to the influence of the Soviet Union and China. Each new revolution that began was a threat to the system defended by the United States. In this context, the rise of Vietnam as a defender of communism, coupled with the influence that this revolution could have in neighboring countries of Southeast Asia, caused the United States to support France in the conflict and subsequently, the American Armed Forces entered directly in combat.
Option D is the right answer.
The Montgomery Bus Boycott was a major success of the Civil Rights movement. This boycott was a social and political protest campaign against the doctrine of racial discrimination in public transportation. The boycott began when an African- American lady was imprisoned for denying to quit her chair to a White man. And this protest resulted in the Supreme Court's verdict that claimed the Montgomery and Alabama laws that segregated buses were illegal.
Enforce a stricter code of conduct more closely following the rules and guidelines of the supreme court
A form of government in which a monarch or a group of individuals headed by a supreme ruler possesses absolute power. Autocracy (samoderzhavie) became a specific phenomenon in Russia.