A mountain slope and a skier make up a closed system with 21,800 J J of energy. When the skier starts her descent down the mountain, the mechanical energy of the system is 19,500 J. By the time she reaches the bottom, the system's mechanical energy has fallen to 18,230 J. How much of the total energy is transformed into thermal energy?
A. 2,300 J
B. 3,570 J
C. 20,530 J
D. 1,270 J