B. To determine when a product should be sold, we need to look at the costs to manufacture further and the incremental revenue that will be received by manufacturing further. The joint costs up to the split-off point are irrelevant in this decision as they are sunk costs.

C. To determine when a product should be sold, we need to look at the costs to manufacture further and the incremental revenue that will be received by manufacturing further. The costs incurred after the split-off point are the costs of further manufacture and are therefore relevant to this decision.

D. To determine when a product should be sold, we need to look at the costs to manufacture further and the incremental revenue that will be received by manufacturing further. The sales salaries for the period are not relevant costs.