Suppose That Unit Costs Are the Same at Both 100

Suppose that unit costs are the same at both 100 units of output and 150 units of output. Unit costs are higher at output levels less than 100 units and at output levels greater than 150 units. It follows that minimum efficient scale exists

A) somewhere between 100 and 150 units.
B) at 100 units.
C) at 150 units.
D) at less than 100 units.
E) at greater than 150 units.