Which of the following statements is true?
A) Friction is a conservative force and does negative work.
B) Potential energy may be defined by the equation U(x) = -dF(x)/dx
C) The work done by a conservative force between two points depends on the path taken between those points.
D) A conservative force cannot change a body's total energy.
E) The work done by a conservative force while a body moves at constant velocity must be zero.