Which of the Following Is Not a Suggested Reason for the Adaptive

Which of the following is not a suggested reason for the adaptive radiation of silverswords on the Hawaiian archipelago?

A) Water is an effective barrier for many organisms.
B) Because islands are small compared with mainland areas, more species would be expected to develop there.
C) Competition is frequently reduced on islands.
D) More ecological opportunities exist on islands that have not been colonized by many species.
E) Neither b nor d is a suggested reason.