Question

After twenty years of US involvement in Vietnam, many Americans agreed with the counterculture and

Answer 1

The answer is B worried about Communist aggression in Vietnam

Answer 2

Counterculture refers to a movement where most of a generation presents different values and political positions than the previous ones. For example, the counterculture in 60s and 70s in the United States was held by the Hippie movement. Contrary to their parents, who grew up during World War II and saw war as a valid option, the counterculture didn't support the war and their  influence expanded quickly among the American population, so people began to question both the war and the fairness of the draft (option D).