Refer to Exhibit 31-1. This graph represents a negative externality situation. Given this, which of the two curves, X or Y, represents marginal social costs and why? Group of answer choices Curve X, because if there is a negative externality, external costs are associated with it: social costs = external costs + private costs, therefore the marginal social cost curve must lie above the marginal private cost curve. Curve Y, because if there is a negative externality, negative external costs are associated with it: social costs = negative external costs + private costs, therefore the marginal social cost curve must lie below the marginal private cost curve. Curve X, because if there is a negative externality, external benefits are associated with it: social costs = external benefits + private costs, therefore the marginal social cost curve must lie above the marginal private cost curve. Curve Y, because if there is a negative externality, negative external benefits are associated with it: social costs = negative external benefits + private costs, therefore the marginal social cost curve must lie below the marginal private cost curve