What is a closed class system? Example of a closed class system?

A classic example of a closed-class society without social mobility is the Hindu society under the caste system. ... In a closed-class society there is pronounced tendencies toward radicalism and revolution. A closed-class society is one in which position is fixed at birth and cannot be changed by individual achievement.

Explanation:

where's the excerpt?   also i think the answer is the last one

interact. i am not 100% sure with this, but you can communicate without speaking, so i think interacting is more precise answer.