One of the answer choices contains a clear subject-verb agreement error. Three of the five answer choices highlight what I call a “Style” error. An answer choice contains a Style error when it is grammatically fine, but is overly complicated, awkward, ambiguous, or redundant. It is important to note, however, that you can only evaluate Style errors when you have eliminated all other errors of meaning or grammar. I often tell my classes: “Meaning trumps grammar, and grammar trumps style.”
Answer choice A can be eliminated for a concrete subject-verb agreement error. Since the subject of the sentence (“crude oil and natural gas”) is compound, the verb must take the plural form. The reason why the singular form sounds fine to most people’s ears is because the part of the subject closest to the verb (“crude oil”) is singular. But the “and” separating the two parts of the subject forces the plural form. Period. This is a deliberate trap set up to confuse test-takers. The sentence could correctly read, “There are crude oil and natural gas supplied…” Answer choice A can be eliminated.
Answer choices B, D, and E are all grammatically okay. They sound a little convoluted, but they cannot be eliminated because of grammar or meaning issues alone. All three of these answer choices contain a Style error type called passive voice (when the subject is not the “doer” of the verb, but is being “done to” by the verb.) Note that passive voice is perfectly legal from a grammatical standpoint. The GMAT sometimes even includes passive verb voice in correct answers to confuse test-takers. But because the remaining answer choices do not contain substantial grammatical or meaning errors, we can use passive verb voice as potential leverage to eliminate answer choices.
Answer choice C is straightforward. It correctly avoids subject-verb agreement errors and uses active voice. (Notice in answer choice C that the subject “Pipeline System” is the “doer” of the verb. The “Pipeline System supplies crude oil and natural gas.”) C is the correct answer.