Only need the solution for (b) and (d).

1. Prove or disprove each claim below: (a) If A is decidable and B is decidable, then AUB is decidable. [5] (b) If AUB is decidable, then A and B are decidable. [5] (c) If A is decidable and B is decidable, then An B is decidable. [5 (d) If AnB is decidable, then A and B are decidable. [5]