A mass attached to the end of a spring is pulled out and released on a surface with friction. The work Fsp · dx done on the mass by the force exerted by the spring

a. has the same sign as the change in energy owing to friction during one half of each cycle.

b. always has the same sign as the change in energy owing to friction if the force of friction is greater than the spring force.

c. never has the same sign as the change in energy owing to friction.

d. never has the same sign as the change in energy owing to friction if the force of friction is greater than the spring force.

e. always has the same sign as the change in energy owing to friction.