Select A,B
From R1, R2 :
In this query first we will take cartesian product of R1, R2 (R2 must be non empty)for this 0- R2 then select distinct A,B from Cartesian product of R1, R2 (for A,B being distinct there should not any duplicate A,B).
And
Select A,B
From R2
For this query A,B → No duplicate A,B.
By combining condition for both query we will get the right condition.
So, option (B) is correct.