Question Completion Status O d(Swallows, Sunday) QUESTION 12 The relation R(a,b) may have duplicate tuples. Which of the following queries has a result that is guaranteed not to have duplicates, regardless of what tuples R contains? O a.SELECT b FROMR WHERE aIN (SELECT b O b.SELECT* WHERE a b; OC.SELECT AVG(a) FROMR d SELECTb, MAXIa) FROMR QUESTION 13 Suppose relations R(AB) and S(B.C,D) are as follows