Answer
(B)
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 $\$ 1000$ to $\$ 0$,
so they ( $C^{\prime}$ ) are decreasing on this interval.
2. From x=110 onward, the slope is becoming steeper ( $C^{\prime}$ increases)
The choice that best describes this is (B).
