Answer:
b. All three countries have a majority population belonging to the Khmer ethnic group.
Step-by-step explanation:
During the colonial era, French Indochina was made up of the countries like Cochin-China, Annam, Cambodia, Tonkin, Kwangchowan, and Laos. These same regions are now divided into the nations of Vietnam, Laos, and Cambodia. On the other hand, Vietnam has a population of 1.5% of people belonging to the "Khmer ethnic group", 97% in Cambodia, and 4000 people belonging to the "Khmer" ethnic group Laos. In the Vietnam War, Vietnam was allied with Cambodia and Laos.