The correct option is A A is true and R is the correct explanation of A.
The whole process of teaching and transmission of Vedas was limited to a small priestly class, who taught and learned the Vedas. They alone were allowed to perform the vedic rituals and accept the tributes and sacrifices as part of the rituals. Over a period of time, they developed into a hereditary class or caste of priests called the Brahmins.
The whole knowldge of Vedas was prohibited to the other classes, especially the Shudras. Shudras were the working class, forming the majority of the society.