TOEFL Reading: ETS-TOEFL阅读机经 - CHI715RG373P16S5L$

In paragraph 4, why does the author point out that crabs and other arthropods were already living on land when the ancestors of the first tetrapods began living there? A. To account for the presence of dead fish along the edges of ponds and streams during the Devonian B. To support the claim that climate change caused freshwater habitats to become more restricted during the Devonian C. To identify a consequence of the emergence of plants into terrestrial habitats near ponds and streams D. To identify a possible reason for why certain fish gradually became terrestrial organisms