Table 84 -Refer to Table 8

Multiple Choice

Table 8.4
$\begin{array}{cc}\begin{array}{c}\text { Quantity } \\\text { of Output }\end{array} & \text { Market Price (\$) } \\\hline 0 & 0 \\10 & 5 \\20 & 5 \\30 & 5 \\40 & 5 \\50 & 5\end{array}$
-Refer to Table 8.4,which shows the output supplied by a firm and its total revenue.When does marginal revenue start decreasing?

A) at a quantity of 10
B) at a quantity of 20
C) at a quantity of 30
D) at a quantity of 40
E) It stays constant at MR=P.