Which Person Has the Highest Opportunity Cost of Obtaining a College

Which person has the highest opportunity cost of obtaining a college degree (assuming that attending college requires giving up his or her current position) ?

A) Bill, who is unemployed.
B) Jane, who is an unwed mother and earns $15,000 a year.
C) Larry, who is a technician in the navy earning $18,000 a year with free food and housing.
D) Mary, who has a job earning $60,000 a year as a computer programmer.
E) Unable to determine from the data given.