How is C Wrong

Hey there, thanks for your post. The stimulus presents an argument. According to the oil analysts, if the price of oil falls by half, consumer's purchase price for gas will also fall by half. You are asked to cast doubt on this prediction. Note that the oil analysts' reasoning is cause & effect. Answer choice (E) does so by establishing (if true) that the price of gas has much more to do with costs other than the price of oil (i.e., refining costs, distribution costs, and taxes). This answer choice presents an alternative "cause" for the price of gas - costs other than the price of oil. Answer choice (C) is neutral. Even if there are many gas companies, it could still be true, according to the oil analysts, that an increase in the price of oil would lead to an increase in the price of gas across the board - meaning that all gas companies would see gas prices go up, and even if they competed to try to give consumers the lowest possible price, they'd still be dealing with higher base prices. Hope this helps! Please let us know if you have any additional questions.

@Mehran How can i easily identify which ones are cause and effect? I can never figure out which ones are and which ones are just sufficient and necessary

Generally, cause and effect is often a subset of sufficient and necessary. The key is to look for conditional logic indicators, which tell you whether or not what you're looking at has conditional logic in it. In this case, the word "if" is a conditional logic indicator, so the sentence in the stimulus contains conditional logic.