Because of friction

Responses
A energy is NOT always conserved.energy is NOT always conserved.
B NOT all potential energy is converted to kinetic energy.NOT all potential energy is converted to kinetic energy.
C all of an object's kinetic energy turns into potential energy.all of an object's kinetic energy turns into potential energy.
D all of an object's potential energy turns into kinetic energy.

B NOT all potential energy is converted to kinetic energy.