There Is Less of a Principal-Agent Problem Between Managers and Apple

There is less of a principal-agent problem between managers and apple pickers than between managers and secretaries because

A) apple pickers naturally work harder
B) secretaries get paid less than their worth
C) productivity is easier to measure in apple picking than in secretarial services
D) a secretary's marginal product is easier to estimate than an apple picker's
E) managers can watch apple-pickers more closely than they can secretaries