In 2016, the top-selling pharmaceutical drug in the world was AbbVie's Humira, which is used for the treatment of several common, chronic conditions. The majority of its profits are derived from treatment of the most common diseases, but AbbVie also develops drugs for rare conditions.

Why might AbbVie develop drugs for rare diseases instead of investing all of its resources toward drugs for common diseases?

It is possible that

A. the interdependence principle may be guiding AbbVie to develop and produce drugs for rare conditions. Common chronic and rare conditions are often experienced by the same people, so AbbVie can easily produce drugs for both.

B. framing effects may be enticing AbbVie to develop and produce drugs for rare conditions. Since these drugs are more expensive, AbbVie will make a large profit.

C. the marginal principle may be guiding AbbVie in determining if it is worth producing drugs for rare diseases. Since it is developing and producing treatments for rare diseases, the marginal benefits must exceed the costs.

D. the opportunitycost principle may encourage AbbVie to produce drugs for rare conditions, because the full benefits outweigh the costs. The company must be maximizing its total economic surplus.