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 inline 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.