Answer: A. The characters should speak grammatically correct sentences
Explanation: Not 100% sure, but it makes the most sense. It wouldn't be very important to speak in short sentences, and based on the tone/mood of the current scene a character might not respond to another. Also in storytelling, it isn't really important at all that the characters speak politely. Hope this helped.
Dialogue using the character's own words is one way a writer can show rather than tell readers what a character is like. Dialogue involves summarizing what characters say to help the story move along more quickly.