Remember, the main point of an argument will never lead us to, i.e. support, any other sentence in the passage. In fact, every sentence in the passage will in some way support the main point.
We are told that "Some people claim that the battery powered electric car represents a potential solution to the problem." But, we are given explanations as to why this is not the case, because "increasing the number of electric cars on the road would require building more generating facilities since current facilities are operating at maximum capacity."
Ultimately, we are told that even if all the gasoline powered cars on the road were replaced by electric cars, "it would at best be an exchange of one source of fossil fuel pollution for another."
Thus, every statement in the argument supports or points to the fact that battery powered electric cars are not a viable solution to the problem of air pollution, i.e. answer choice (D).
Hope that was helpful! Please let us know if you have any other questions.
