Explanation
A. The fact that most non-extinct plants are native to mainland regions does not directly support the explanation for why island plants have gone extinct at a faster rate.
B. Whether non-native plant species have become well established on islands is not relevant to the argument concerning the extinction of native island plants due to lack of defenses against large land mammals.
C. Commercial development leading to habitat loss does not address the specific claim about the lack of defenses in island plants against large land mammals.
D. (Correct Response) If the rate of extinction of native plant species on an island increases after human colonization, this supports the biologists' explanation that the introduction of large land mammals (which often occurs with human colonization) could be a significant factor in the extinction of island plants that lack defenses against such mammals.
E. The preference of large land mammals for mainland plants over island plants is not directly related to the argument about the extinction of island plants and their lack of defenses against these mammals.
The statement that most strongly supports the biologists' explanation is option D, which directly ties the increase in the extinction rate of native island plants to the period following human colonization, suggesting a link between human colonization, the subsequent introduction of large land mammals, and the extinction of native plants lacking adequate defenses.