Answer:
The most effective counter argument to the statement "With diminishing school budgets, gym class is not as important as core courses" is the following one: C)Gym classes allow students to maintain mental and physical health and serve to support academics. A counter argument is used when one wants to express his or her disagreement towards a certain point of view. However, a counter argument also aims at trying to make someone change his or her mind by providing supposedly better arguments to address a certain issue or topic. Therefore, by pointing out the mental and physical benefits that gym classes bring, one is, in other words, saying that they are indeed important and must not be regarded as inferior to other subjects nor should they be considered as an option when it comes to cutting costs.