A set A is a subset of another set B if all elements of the set A are elements of the set B. In other words, the set A is contained inside the set B.
Consider sets A and R:
1. set A consists of seven colors of the rainbow: red, orange, yellow, green, blue, indigo and violet;
2. set R consists of three colors: red, yellow and blue.
As you can see all three colors from the set R belong to the set A, then the set R is the subset of A.
Answer: correct choice is B.
