Refer to Figure 7.5. Diminishing marginal returns set in after the ________ worker is hired.

A) first
B) fifth
C) eighth
D) sixteenth

Diminishing marginal returns occur when adding an additional factor of production results in a smaller increase in output. Without seeing Figure 7.5, the typical context of this concept suggests that after a certain point, adding more workers leads to less efficient production increases. The correct answer, based on the question, is after the fifth worker is hired.