Task: Question Answering
Input (English): Two balls rolled down two identical inclined planes. The balls were exactly the same mass and size, but one ball rolled down the inclined plane faster. Identify a possible reason that one ball rolled faster than the other ball.  
 (A) One ball was red and the other ball was blue. (B) One ball was new and the other ball was old. (C) One ball was shiny and the other ball was dull. (D) One ball was sticky and the other ball was smooth.
Output (English): D