For make-or-buy decisions, relevant costs include:Group of answer choicesdifferential costs plus fixed costsincremental costs plus differential costsincremental costs plus sunk costsincremental costs plus opportunity costs

For make-or-buy decisions, the relevant costs include incremental costs plus opportunity costs.

Here's why:

1. Incremental Costs: These are the additional costs that will be incurred if the decision is made to 'make' the product. These could include costs of additional materials, labor, utilities, etc. These costs are relevant because they will only be incurred if the decision is made to 'make' the product.

2. Opportunity Costs: These are the costs of the next best alternative that is foregone. In the context of a make-or-buy decision, the opportunity cost could be the profit that could have been earned from using the resources elsewhere. For example, if the machinery used to 'make' the product could have been used to produce another product, then the profit from that other product is the opportunity cost. These costs are relevant because they represent potential benefits that are lost.

Fixed costs are not relevant because they will be incurred regardless of the decision. Similarly, sunk costs are not relevant because they have already been incurred and cannot be recovered. Differential costs could be relevant, but they are not necessarily included in every make-or-buy decision.