A boy on a sled is sliding with negligible friction along an icy, horizontal surface. As the sled passes underneath a tree, a large mass of snow falls vertically and lands on the moving sled. Which of the following statements is true?

A. The snow collides elastically with the sled.
B. Linear momentum is not conserved in this example.
C. Kinetic energy is conserved in this example.
D. Linear momentum is conserved in this example.