Which choice completes the text so that it conforms to the conventions of Standard English? A model created by biologist Luis Valente predicts that the rate of speciation-the rate at which new species form-on an isolated island located approximately 5,000 kilometers from the nearest mainland ______blank triple the rate of speciation on an island only 500 kilometers from the mainland.

Choice D is the best answer. The convention being tested is finite and nonfinite verb forms within a sentence. Relative clauses, such as the one beginning with 'that,' require a finite verb, a verb that can function as the main verb of a clause. This choice correctly supplies the clause with the finite future tense verb 'will be.' Choice A is incorrect because the nonfinite participle 'being' doesn't supply the clause with a finite verb. Choice B is incorrect because the nonfinite to-infinitive 'to be' doesn't supply the clause with a finite verb. Choice C is incorrect because the nonfinite to-infinitive 'to have been' doesn't supply the clause with a finite verb.