Join size estimate and join strategy without knowledge of primary key. (9 points) Consider three relations rl, r2 and r3, with schemas R1(ABC), R2(CDE) and R3(EF) respectively (without the knowledge of any primary keys). Assume that nl 3000, n2 4000, and nr3-20. In addition, we also know that V(C, r1) =300, V(C, r2) = 1000, VE, r2) = 40, and VE, r3) = 10. (i) Estimate the size of natural join of three relations rl x r2 Ix r3. (ii) Give an efficient strategy for computing the join. (iii) If we only consider the join of r2 and r3, w that is the estimated size ofthe result