Answer:
Transitional fossils show how a particular taxa accumulated adaptations to fit particular environments and/or ecological niches
Explanation:
Transitional fossils are fossilized remains of taxonomic groups/species that illustrate an evolutionary transition between a known version of a taxa/species and the current taxa/species. Transitional fossils are fundamental because they can be clearly differentiated from the ancestral group as well as of its derived descendant group. For example, there exist transitional fossils known as "mammal-like reptiles"(i.e., therapsids that gave rise to the true mammals), which are clearly different from current mammals.
The answer is basically D
