The correct answer is option D: the Vietcong and North Vietnamese showed that they could still fight.
The Tet offensive was considered a turning point in the Vietnam War because it showed the Vietcong and North Vietnamese could still fight more. It was led by Vo Nguyen Giap who was one of the best generals of the 20th century.
He was trained in guerrilla war tactics, so he planned the offensive and decided to attack on Christmas Eve when it was least expected.
For that reason, Giap attacked two fronts: the US Marines' firebase in Khe Sanh and, at the same time, the NLF and NVA attacked the major cities of South Vietnam. Even though the Tet offensive didn't succeed as expected, it had a deep and lasting effect during the war, which proved to be a turning point.
