Children are in pursuit of a dog whose leash has broken. "A” is directly behind the dog. "B” is behind "A”. "D” is behind "B”. "C” is ahead of the dog walking down the street in the opposite direction. As the children and dog pass, "C” turns around and joins the pursuit. He runs in behind "B”. "A” runs faster and is alongside the dog on the left. "B” runs faster and is alongside the dog on the right. Which child is directly behind the dog?