What is the difference between a monologue and a soliloquy?

A. Monologues have been used for centuries in theater; soliloquies are a relatively recent innovation.
B. Monologues tend to be longer and more philosophical; soliloquies are more brief and emotional.
C. Soliloquies usually involve more than one character; monologues involve a character alone onstage.
D. Soliloquies involve a character talking to herself; monologues may be addressed to someone.