A certain cost function has the following graph:
a. The associated marginal cost is
(A) increasing, then decreasing
(B) decreasing, then increasing
(C) always increasing
(D) always decreasing
b. The marginal cost is least at approximately
(A) $x=0$
$\begin{array}{lll}\text { (B) } x=50 & \text { (C) } x=100 & \text { (D) } x=150\end{array}$
c. The cost of 50 items is
(A) approximately $\$ 20$, and increasing at a rate of about $\$ 3,000$ per item
(B) approximately $\$ 0.50$, and increasing at a rate of about $\$ 3,000$ per item
(C) approximately $\$ 3,000$, and increasing at a rate of about $\$ 20$ per item
(D) approximately $\$ 3,000$, and increasing at a rate of about $\$ 0.50$ per item