Which was not an effect of the Tet offensive?

The attitude of millions of Americans toward involvement in the war changed when they saw that the Vietcong were stronger and more numerous than Americans had been led to believe.

U. S. forces dealt the Vietcong a massive military loss and regained control of all areas that the Vietcong had attacked.

The strength shown by the Vietcong led millions of Americans to become more critical of Johnson and his handling of the war.

Vietcong casualties were very low, while American casualties were relatively high.

When it was over, the Viet Cong basically ceased to be an effective force any longer. Their ranks were decimated. All of the territory lost during the offensive was shortly won back. But the ability of the Communists to launch such a widespread coordinated offensive convinced the American media and ultimately the American public that the war was now a lost cause and demanded a withdrawal. So, tactically, it was a military success for the U. S. but it served as a public relations success for North Vietnam.

I believe the answer may be

U. S. forces dealt the Vietcong a massive military loss and regained control of all areas that the Vietcong had attacked.