Answer:
b. Causing many Americans to question whether or not the U.S. could win.
Step-by-step explanation:
While the Tet Offensive is a major strategical & military victory, it led to the US public outrage that they were lied to by the media and the government that the North was almost soundly beaten. This event led to large amounts of protests and even riot to bring American troops back home in what they believed to be a "unwinable war". Eventually, the US government listened to the people's demand, and withdrew support from South Vietnam, which led to their eventual downfall.
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