Which of the Following Individuals Is Demonstrating an Optimistic Outlook

Which of the following individuals is demonstrating an optimistic outlook on life?

A) Cary, who gets angry when his favorite baseball team is losing a game.
B) Carlotta, who has had enough of her job and doesn't feel it will ever make her happy.
C) Carla, who is in a relationship that is just "for now" while waiting for the love of her life.
D) Carl, who tends to see the good in situations and always looks on the bright side of things.