The Following Data Show the Total Output for a Firm

The following data show the total output for a firm when different amounts of labour are combined with a fixed amount of capital.Assume that the wage per unit of labour is $10 and the cost of the capital is $50.
TABLE 7-3
-Refer to Table 7-3.The average product of labour is highest when the firm hires

A) 1 unit of labour.
B) 2 units of labour.
C) 3 units of labour.
D) 4 units of labour.
E) 5 units of labour.