Read the following passage taken from Oxford Advanced Learner’s Dictionary, 8th edition, and mark the letter A, B, C, or D on your answer sheet to indicate the correct word for each of the blanks from 56 to 65. THE VIETNAM WAR    Like the Korean War, the Vietnam War was a result of US policy during the Cold War, a period when Americans believed that Communism, the political system in the Soviet Union and China, was a threat to their ___(56) ___ and power.    Vietnam, a colony of France, wanted to become independent, but the US believed that Communists were behind the ___(57) ___ movement, and so opposed it. The US became ___(58) ___ in Vietnam only gradually. At first, under President Eisenhower, it provided the French with supplies. In 1954 the Geneva Accords divided Vietnam into the Communist North and the anti-Communist South. Under President Kennedy, in the early 1960s, many US soldiers were sent to the South ___(59) ___ advisers. In 1964, after an attack on US ships, Congress passed the Gulf of Tonkin Resolution which gave President Johnson greater powers to fight a war, and in the spring of 1965 Marines were sent to South Vietnam.    It was easy to keep the Communist forces, called the National Liberation Front or the Viet Cong,___(60) ___ South Vietnam, but much ___(61) ___ to defeat them. The US used bombs against the Vietnamese troops, and chemicals to destroy crops, which had a terrible effect on people as well as on the land. There were also reports of atrocities (= acts of extreme violence and cruelty ) committed by both sides. In 1968 the My Lai massacre, in which over 300 civilians were killed by US soldiers, ___(62) ___ Americans at home. Many US soldiers were not sure ___(63) ___ they were fighting the war and became traumatized by the violence around them. Discipline became a problem, and the use of drugs was common. Soldiers were accused of committing acts of violence against each other and against Vietnamese civilians.     In 1968 the Viet Cong started a major attack, and the US position in South Vietnam was threatened. As the war escalated it lost support at home and also in other countries. When Richard Nixon became President he ___(64) ___tried to attack hard and force the Viet Cong to come to an agreement. The war then spread to Vietnam’s neighbour, Cambodia. Finally, in 1972, Nixon sent Henry Kissinger to negotiate a ceasefire, and afterwards the US was no longer directly involved in the war, though it continued to provide supplies. In 1975 the government of South Vietnam fell and the country was ___(65) ___ by the Communist forces. Trả lời câu hỏi dưới đây:________(56)