Three students determine the gravitational potential energy of an object at a given location. Student A says the gravitational potential energy is positive in value, student B says it is zero in value, and student C says it is negative in value. Which of these students can be correct?
a. only student C.
b. only student B.
c. all of the students.
d. only student A.
e. either student A or B, but not student C.