Solution:

Provided that

A {1, 2, 3, 4}, B {3, 4, 5, 6}, C {5, 6, 7, 8} and D {7, 8, 9, 10}

(i) A ∪ B {1, 2, 3, 4, 5, 6}

(ii) A ∪ C {1, 2, 3, 4, 5, 6, 7, 8}