Which of the following would best model the Doppler effect?
A. A toy boat moves through a small pool. The water waves around the boat appear to bunch together in front of the boat and spread further
apart behind the boat.
B. A strobe light flickers on and off in a room, causing people to appear to move more slowly.
C. A pencil is held loosely at one end and is moved up and down. This motion creates the illusion that the pencil is made of rubber.
D. A person on a moving train observes that a book is at rest, but a person observing the train from a stationary platform observes that the book
is in motion.