1.A = set of odd numbers, B = set of even positive numbers, C = set of even negative numbers.
Here A, B and C are infinite sets, but A∩(B U C) is ∅ which is finite.
2. : x =1+⎷2 y=1-⎷2x and y are irrational, but x+y is 2, which is rational.
So both S1 and S2 are correct.