Which of the Following Is the Best Example of an Investment

Which of the following is the best example of an investment in human capital?

A) an increase in the number of hours worked per week by worker in a job employing low-skilled labor
B) the purchase of company stock by a worker
C) a summer internship at a law firm filled by someone attending law school
D) payments into a retirement pension plan by a skilled laborer
E) the purchase of a vehicle by an employee in order to commute to work