Refer to Exhibit 30-1. If the exhibit represents a negative externality situation, then what is Q1?

A. It is the quantity of output at which marginal social costs (MSC) equal marginal private costs (MPC).
B. It is the quantity of output at which MPC > MSC.
C. It is the market output; it is the quantity of output that exists if the external costs associated with the negative externality are not taken into account.
D. It is the socially optimal output; it is the quantity of output that exists if the external costs associated with the negative externality are taken into account.
E. none of the above