Marcel takes out student loans and works part time to put himself through college. In time, he earns an advanced medical degree and goes to work in an understaffed city hospital. Marcel's economic decisions benefit the goal of efficiency by __________.A. Making his own job-related decisions.
B. Paying back loans to reduce the debt.
C. Contributing to the nation's productivity.
D. Taking advantage of equal opportunities.

According to the question, Marcel's way of working as part time employee for lessening student loan and gaining further medical degree to work in hospital is a measure to be a part to increase productivity of nation .Working part-time ,advanced studying etc is the input that is converted into useful output for nation's productivity.

Other options are incorrect because taking benefit from equal chance scheme, repay of loan and taking job decision for own self are not the methods followed by Marcel to be a part of economic efficiency.Thus, the correct option is option(c).