The tet offensive showed americans that

the u. s. policy in vietnam was effective
the united states was close to victory in vietnam
in contrast to what they were told, the north vietnamese and nlf were not finished
the south vietnamese army needed more training

Option C. The Tet Offensive showed Americans that in contrast to what they were told, the North Vietnamese and NLF were not finished.

Explanation:

The Tet Offensive was a coordinated series of planned attacks from North Vietnam and NLF launched on January 30th 1968, to more than 100 cities in South Vietnam.  The offensive was an attempt to encourage South Vietnamese citizens and soldiers to join the revolution and for the United States to scale back. Although not many South Vietnamese forces with the aid of the United States troops managed to control the situation, the attacks were a major surprise for the American public, who had been told by the government that the war was virtually over and that the NLF was almost finished. The Tet Offensive was the beginning of the American's public opinion turning anti-war and demanding its government to finish its involvement in Vietnam.

the correct answer is b.