题目选项分析

By the late 1960s, the rising number of American casualties in Vietnam and the 1968 Tet Offensive, the Viet Cong's coordinated surprise attack on American installations throughout the whole of Vietnam, suggesting that Vietnam was an ultimate unwinnable situation for the United States

By the late 1960s, the rising number of American casualties in Vietnam and the 1968 Tet Offensive, the Viet Cong's coordinated surprise attack on American installations throughout the whole of Vietnam, suggested that Vietnam was an ultimately unwinnable situation for the United States