The correct answer is (A).
(A) Inference
Step 1: Identify the Question Type
Treat a question that asks you to fill in the blank at the end of an argument with a conclusion as an Inference question. The correct answer, when tagged onto the argument, should fall neatly within the scope of what has already been stated.
Step 2: Untangle the Stimulus
Proponents of the electric car believe that because the cars are emission-free, their wide use will result in less environmental degradation from auto emissions. In contrast (indicated by the Keyword [b]ut), the author points out that the electricity to charge electric car batteries will come from hydroelectric dams, nuclear energy, or coal power plants, all of which produce considerable environmental damage. Then, the author makes a conclusion regarding the electric car that you must complete.
Step 3: Make a Prediction
Do not get too creative when adding a conclusion at the end of an argument. Typically, the answer should be consistent with what has already been stated or flow from a logical deduction. In this case, complete the contrast that the author is setting up. Proponents of the electric car believe that they will reduce environmental damage from car emissions, but the author points out an indirect way electric cars will continue causing environmental damage. When assessing answers, remember to treat this like an Inference question and be very wary of answers that are Out of Scope or Extreme.
Step 4: Evaluate the Answer Choices
(A) is correct. It completes the disagreement the author has with the proponents of electric cars. This type of modest, safe answer is exactly what you want in an Inference question. The author must believe this is true because the proponents don't consider a negative result that he sees.
(B) is an Irrelevant Comparison. It speculates about the future popularity of electric cars versus other cars, which you cannot determine. This argument is merely about the environmental effects of electric cars.
(C) is a Faulty Use of Detail. This refers to the first sentence, which details the proponents' view, not the author's. Additionally, success and its requirements are Out of Scope.
(D) is Extreme. While the author does not believe that electric cars are emission-free, due to their indirect effect on emissions, the author does not go so far as to claim that electric cars will increase the total emissions currently being released.
(E), while slightly more modest than (D), is also Extreme. It must be true that the author believes the electric car will not produce as great a reduction in environmental degradation as the proponents of electric cars believe. Nevertheless, the author's statements leave open the possibility that the electric car could, on balance, be at least a little better for the environment than gasoline-powered cars.
