If a management accountant is trying to decide whether a cost is relevant to a decision, he or she should consider the cost relevant if:

A) it is a historical cost precise in nature.
B) it is a historical cost that is the same among all alternatives.
C) it is an expected future cost that is the same for each alternative.
D) it is an expected future cost that is different for each alternative.

When considering whether a cost is relevant to a decision, the management accountant should focus on expected future costs rather than historical costs. In addition, a cost is relevant if it is different among the alternatives being considered, as it may impact the decision-making process. Therefore, option D - an expected future cost that is different for each alternative - is the best choice. Options A and B are incorrect because they focus on historical costs, which may not be relevant to the decision at hand. Option C is incorrect because it assumes that the cost is the same for each alternative, which means that it would not impact the decision-making process.