When Oliver sees a girl he knows in costume as a firefighter, if he compliments her costume and talks to her about having an aunt who is a female firefighter, what does this tell you about Oliver's understanding of gender constancy?
A. Oliver understands his friend is still a girl despite wearing a traditionally masculine costume.
B. Oliver can give an example of another female firefighter to his friend.
C. Oliver believes the friend he is talking has transformed into a boy.
D. Oliver cannot tell whether his friend is a boy or a girl.