The wings of auks (alcidae), used for swimming, are called an exaptation because:

A. in the ancestor, wings were used for flight, but they also function well in water.
B. individuals that do not use their wings for swimming have lower fitness.
C. female auks are more attracted to swimming males than flying males.
D. they are useful, but don’t affect fitness. they have a de novo form that was not present in ancestors.