Consider the Following Production and Cost Schedule for a Firm

Consider the following production and cost schedule for a firm.The first column shows the number of units of a variable factor of production employed by the firm. $$\begin{array} { | c | c | c | } \hline \begin{array} { c } \text { Total Numb er of } \\\text { Units of theF actor }\end{array} & \begin{array} { c } \text { Total Number of } \\\text { Units of Output }\end{array} & \begin{array} { c } \text { Price per Unit } \\\text { of Output }\end{array} \\\hline 10 & 20 & \$ 10 \\\hline 11 & 44 & \$ 10 \\\hline 12 & 64 & \$ 10 \\\hline 13 & 78 & \$ 10 \\\hline 14 & 84 & \$ 10 \\\hline 15 & 86 & \$ 10 \\\hline\end{array}$$ TABLE 13- 1
-Refer to Table 13- 1.Diminishing marginal returns are present for which units of the factor of production?

A) 11th unit only
B) 10th unit only
C) 13th unit only
D) 12th unit only
E) all units shown in the table