Table 72 -Refer to Table 7

Multiple Choice

Table 7.2
$$\begin{array} { c c } \text { Labor } & \begin{array} { c } \text { Total Froduct } \\\text { (pairs of shoes) }\end{array} \\\hline 0 & 0 \\1 & 20 \\2 & 50 \\3 & 75 \\4 & 80 \\5 & 75\end{array}$$
-Refer to Table 7.2,which shows labor and the quantity of shoes produced by a firm.At which points do negative marginal returns set in?

A) before the first unit of labor
B) between the first and second units of labor
C) between the second and third units of labor
D) between the third and fourth units of labor
E) between the fourth and fifth units of labor