The Table Below Shows the Total Production for Varying Numbers

The table below shows the total production for varying numbers of hours worked producing yo- yos.The firm sells its product and hires its workers in competitive markets. $$\begin{array} { | c | c | c | c | } \hline \begin{array} { c } \text { Number of } \\\text { Hours Worked }\end{array} & \begin{array} { c } \text { Number of } \\\text { Yo-Yos } \\\text { Produced }\end{array} & \begin{array} { c } \text { Wage Rate } \\\text { per Hour } ( \$ ) \end{array} & \begin{array} { c } \text { Price of Yo- Yos } \\( \$ ) \end{array} \\\hline 10 & 60 & 10 & 5 \\\hline 11 & 70 & 10 & 5 \\\hline 12 & 78 & 10 & 5 \\\hline 13 & 84 & 10 & 5 \\\hline 14 & 88 & 10 & 5 \\\hline 15 & 90 & 10 & 5 \\\hline\end{array}$$ TABLE 13- 4
-A perfectly competitive firm will continue to increase production until the marginal cost of the variable factor is

A) less than the marginal revenue of the firm's output.
B) equal to zero.
C) equal to the marginal revenue of the firm's output.
D) equal to the marginal revenue product of the factor.
E) greater than the marginal revenue of the firm's output.