Ram and Shyam are pushing two identical boxes. Ram is pushing box I that is placed on a wheel cart, while Shyam is pushing box II that is placed on the ground. Both Ram and Shyam are trying to maintain a steady motion of the boxes. It is relatively difficult for Shyam to maintain a steady motion of box II because

• A.  Sliding friction is greater than rolling friction
• B.  Rolling friction is greater than sliding friction
• C.  Static friction is greater than sliding friction
• D.  Sliding friction is greater than static friction