Which of the following statements is correct regarding relevant and irrelevant costs and benefits for decision-making?

a) Variable costs should always be considered relevant costs for decision-making.

b) Future costs that do NOT differ between alternatives in a decision are avoidable costs.

c) A cost that is relevant in one decision can be regarded as relevant in other decisions.

d) A cost that will be incurred regardless of which alternative is selected is NOT relevant when choosing among the alternatives.