I think B is not equals to the rest of the choices, but I don't know how to prove it

(10 points) Consider two simple relations R1(A, B ) and R2( B , 0). Which of the following relational algebra expressions is not equivalent to the other three? Provide a counterex ample to show that your selected choice is not equivalent to one of the other three choices. The counterexample should include a data instance where the two compared relational algebra expressions return different results (to prove the inequivalence). 13- 7r.a1,s(R1 W Ra) B. R1 N (WB{R2)) c. 31