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) secretaries receive on-the-job training, but apple pickers receive no such training.