A swim bladder is a gas-filled sac that helps fish maintain ...

[penguins]

A swim bladder is a gas-filled sac that helps fish maintain buoyancy. The evolution of the swim bladder from lungs of an ancestral fish is an example of
A) an evolutionary trend.
B) exaptation.
C) changes in Hox gene expression.
D) paedomorphosis.
E) adaptive radiation.

[Millan]

I know it's B, we did this yesterday

[penguins]

Thank you, thank you!!