Which of the following students may have education expenses eligible for the American Opportunity Tax Credit?

A. Isaac (55), a full-time undergraduate degree candidate at a state university who completed a four-year degree program in 1986.

B. Deborah (45), a full-time undergraduate degree candidate at a state university who has not previously completed a four-year degree.

C. Patricia (15), a full-time student attending a private high school.

D. Robert (23), an undergraduate degree candidate at a state university attending less than half-time.