It is called a Coordination. Hope this helps!
Answer:
C: John, you look sick. What's wrong?
Explanation:
While all the other sentences only manifest opinions, suggestions, and decisons already made concerning John's condition and care, even some despair, the sentence in C, besides mentioning his appearance, also allows John to<em> express what or how he is feeling by asking</em> 'what's wrong?', which is a form of <em>dialogue</em>, and the inclusion of someone's opinion.