Answer (A) is correct.
Joint products are created from processing a common input. Joint costs
are incurred prior to the split-off point and cannot be identified with a
particular joint product. As a result, joint costs are irrelevant to the
timing of sale. However, separable costs incurred after the split-off point
are relevant because, if incremental revenues exceed the separable costs,
products should be processed further, not sold at the split-off point.