Net exports are defined as the value of a country's total exports minus the value of its total imports. Therefore, the correct answer from the options provided is:
d. imports minus exports.
However, it's worth noting that the common way to represent net exports can also be "exports minus imports," which is the conventional formula used in economics. If you meant to state that you are looking for exports minus imports, that would traditionally be referred to as "net exports." In this context, "d" suggests it in an opposite form. However, if we consider the need for a negative sign, this might mislead the interpretation.
If you have more contexts regarding how net exports are calculated or the perspective from which the question was asked, please provide it for better clarity.