Joshua is a young male who engages in an imaginary game with other children his age in your clinic's play area. When his father enters the play area to pick him up, Joshua tries to involve him in the game, acting as if he is another full participant. When the father makes it clear he is not involved, Joshua stops playing immediately. Joshua is in which of Jean Piaget's four stages of development?
A. Preoperational
B. Concrete operational
C. Sensorimotor
D. Formal operational