A factory is situated next to a dormitory for nurses who work night shifts. The factory produces $120$ humanoid robots a day. The production process is rather noisy, and the nurses often complain that their sleep is disturbed. Based on this information, which of the following statements is correct?

Question $1$ options:

The marginal social cost is the noise cost incurred by the nurses from production of an additional robot.

The marginal private cost is the factory's total cost of producing $120$ robots a day.

The marginal external cost is the cost to the factory, plus the noise cost incurred by the nurses, when an additional robot is produced.

The total external cost is the total costs per day imposed on the nurses by the factory's production.