By the late 1960s, most Americans
O supported the president's approach in Vietnam
O understood the goals of the US in Vietnam
O considered the cost of war to be justified by the results.
O had begun to question the cost of the Vietnam War

They had begun to question the cost of the Vietnam War.

Explanation:

By 1969, opposition to war had rose. American cities were the scenarios of mass rallies and marches for peace and a withdrawal from Vietnam. The public was worried about the high number of casualties and the economic costs of the war.

They did not see the purpose of fighting and were increasingly distrustful of the official version told by civilian and military officials, especially after the images of North Vietnam´s Tet Offensive of 1968 revealed chaos and uncertain perspectives of victory.

social contract theory, nearly as old as philosophy itself, is the view that persons' moral and/or political obligations are dependent upon a contract or agreement among them to form the society in which they live