It was replaced by the Russian tricolor
The answer is D. The Treaty of Versailles forced Germany to accept sole responsibility for the war and to pay heavy compensation to all countries involved.
America's view in the Vietnam was fear. Fear drove them to participate in the war. Why fear? They were afraid Vietnam would become communist because if they became communist they would support or have the support from the Soviets. If this were to happen Vietnam could've became a missile launching spot for the soviets if America wouldn't have participated.
It's my best explanation from what I remember and from what I think. Hope it's helpful to you.