Acanthostega is an extinct amphibian. fossils indicate that it had four limbs, lungs, gills, and a tail used to propel itself through water. why are acanthostega fossils considered transitional fossils?

a. they display evidence of a form between an ancient fish and a modern bird.

b. they display evidence of a tetrapod with lungs.

c. they display evidence of gills and a fin-like tail.

d. they display evidence of a intermediate form between a fish and a tetrapod land animal.