If p men working p hours per day for p days produce p units of work, then the units of work produced by n men working n hours a day for n days is

• A. $${p^2} over {n^2} $$
• B. $${p^3} over {n^2} $$
• C. $${n^2} over {p^2} $$
• D. $${n^3} over {p^2} $$