A cylinder rolls up an inclined plane, reaches some height and then rolls down (without slipping throughout these motions). The directions of the frictional force acting on the cylinder are

• A

  up the incline while ascending and down the incline while descending

• B

  up the incline while ascending as well as descending

• C

  down the incline while ascending and up the incline while descending

• D

  down the incline while ascending as well as descending