Answer
(C)
Work Step by Step
The Marginal cost function: $C^{\prime}(x)$, represents the slope of the tangent to the cost function graph at x.
The tangent to the graph at any point has nonnegative slope,
1. From x=0 to about x=110 items the slopes are getting less steep,
from approximately $\$ 1000$/item to $\$ 0$/item,
so they ( $C^{\prime}$ ) are decreasing on this interval.
The minimal slope ( $C^{\prime}$ ) is about 0 when x is about 110.
So, our choice is (C)
