The choice that best describes the difference between a monologue and a soliloquy is:
"In a monologue, a character gives a speech. In a soliloquy, a character believes they are alone."
To clarify, a monologue is typically a speech delivered by one character, which can be directed at other characters or the audience, while a soliloquy is a type of monologue where a character speaks their thoughts aloud, usually believing they are alone, often revealing their inner thoughts and feelings.