Suppose the Accompanying Table Describes the Relationship Between Price and Quantity

Multiple Choice

Suppose the accompanying table describes the relationship between price and quantity demanded for a monopolist.  
$$\begin{array} { | c | c | } \hline \text { Quntity } & \text { Price } \\\hline 1 & \$ 10 \\\hline 2 & \$ 9 \\\hline 3 & \$ 8 \\\hline 4 & \$ 7 \\\hline 5 & \$ 6 \\\hline 6 & \$ 5 \\\hline 7 & \$ 4 \\\hline 8 & \$ 3 \\\hline\end{array}$$ The marginal revenue of the fifth unit of output is:

A) $30.
B) $6.
C) $2.
D) ?$2.