Are structures that evolve in one context but become co-opted for a different functions ?
a. exaptations
b. vestigial organs
c. novel structures
d. adaptations

a. Exaptations

Explanation:

An exaptation is a structure of an organism that originally evolved as a feature to provide adaptation to a certain condition, but which, once consolidated (for example, several million years later) begins to be used and perfected in pursuit of a new purpose, which, sometimes, is not related at all to its original function.

An example is the feathers of birds.  Feathers are an exaptation becasue they  were originated to maintain body temperature more efficiently. However, feathers became later fundamental as a flying structure.