Which choice completes the text so that it conforms to the conventions of Standard English? Dr. Rocío Paola Caballero-Gill is a paleoceanographer. This means that Dr. Caballero-Gill doesn't just study oceans as they are today. She uses chemistry and fossil evidence ______blank oceans as they were in the past.

Choice B is the best answer. The convention being tested is the use of verb forms within a sentence. The nonfinite to-infinitive verb 'to study' is correctly used to form a subordinate clause that indicates what Dr. Caballero-Gill uses chemistry and fossil evidence for (to study oceans as they were in the past). Choice A is incorrect because it results in an ungrammatical sentence. The finite verb 'has studied' can't be used in this way to form a subordinate clause that indicates what Dr. Caballero-Gill uses the evidence for. Choice C is incorrect because it results in an ungrammatical sentence. The finite verb 'studied' can't be used in this way to form a subordinate clause that indicates what Dr. Caballero-Gill uses the evidence for. Choice D is incorrect because it results in an ungrammatical sentence. The finite verb 'studies' can't be used in this way to form a subordinate clause that indicates what Dr. Caballero-Gill uses the evidence for.