Dear student you should ask single question in a thread;
The three countries of Cambodia, Laos, and Vietnam represent Indochina.
located in Southeast Asia to the south of China and to the east of Thailand.
There are numerous religions, but the main religions are prevalent throughout the region ,here Indian traders brought Hindu and Buddhist religions across the ocean from the west.
Here Indian culture and architecture is reflected in temples of Angkor.
In Indochina those who were known as Mon and Khmer occupied the Cambodian area from the North and between A.D 800s and 1200s.
The language of Cambodia is Khmer while the religion is Buddhism while the religion of Loas is also Budishm where the Vietnam resembles China in many aspects including language and shared religious elements of Confucianism, Buddhism, and ancestor veneration.
In terms of economy Vietnam in 2000 economy of $31 billion which was up four times since 1990. Cambodia and Laos had 2000 total GNIs of less than $4 billion each.