Answer:
C) Tet Offensive was considered as surprise attack because the North Vietnamese and the Vietcong mounted a large attack on Tet, the Vietnamese New Year holiday; a day when most didn't expect it.
Step-by-step explanation:
It was a surprise that shook the American government leading to mistrust of the system by the natives. It created so much conflict that the ruling president then was not re-elected to power. Only after the attack did the people realize the magnitude of the battles had been underestimated or the presidency had previously hidden information about the enormity of the battle.
The US and Vietnamese troops both suffered major losses while the US government was weakened and doubted by its peoples.