A Vendor of Used Paperbacks Leaves Stacks of Books on a Table

A vendor of used paperbacks leaves stacks of books on a table in an area heavily traveled by students, with a box for money and a sign that says $5. Most students who take a book place $5 in the box. What is the most likely reason for this?

A) Most college students understand that this economic opportunity will continue to exist only if they are fair.
B) Most college students feel self-conscious in front of the others looking at the books.
C) Most college students are more morally conscious than the average population.
D) Most college students are sensitive to the plight of the vendor profession.