Which one of the following most accurately expressed the main idea of the passage? A. At present, no single hypothesis explaining the latitudinal gradient in numbers of species is more widely accepted than any other. B. The tropical climate is more conductive to promoting species diversity than are arctic or temperate climates. C. Several explanations have been suggested for global patterns in species distribution, but a hypothesis involving rates of speciation seems most promising. D. Despite their differences, the various hypotheses regarding a latitudinal gradient in species diversity concur in prediction that the gradient can be expected to increase. E. In distinguishing among the current hypotheses for distribution of species, the most important criterion is whether a hypothesis proposes a mechanism that can be tested and validated.