The difference between a piece of expository writing and a narrative is option B:
<em> Expository writing communicates fact-based information, while a narrative tells a story.</em>
In an exposition the writer must express himself very clearly and well-structured for the reader to be able to follow the subject without knowing anything about it beforehand.
A narrative text is a story which can be invented and the writer can even include himself as a character.
Sullen means gloomy or in a bad mood. However, cheerful is the opposite (or an antonym) becuase it is an adjective that means to be happy and in a good mood.
