Which of the following is an example of a complex sentence?

A. "Those are my principles, and if you don't like them... well, I have others." (Groucho Marx)
B. "There's a lady wants to see you. Miss Peters her name is." (P.G. Wodehouse, Something Fresh, 1915)
C. "Because he was so small, Stuart was often hard to find around the house." (E.B. White, Stuart Little, 1945)
D. "It must have been tough on your mother, not having any children." (Ginger Rogers in 42nd Street, 1933)