The diagram below shows a manufacturing firm's Long-run Average Cost (LRAC) curve.

Which level of monthly output represents the firm's Minimum Efficient Scale (MES)?
15,000 units15,000\text{ units}15,000 units
90,000 units90,000\text{ units}90,000 units
45,000 units45,000\text{ units}45,000 units
135,000 units135,000\text{ units}135,000 units