The correct answer is C. More characters would have to appear.
Step-by-step explanation:
In literature, a dialogue takes place when two or more characters interact and share ideas, because of this, a dialogue is only possible if there are at least two characters that speak between them. In the case of the passage presented, there is only one character who is also the narrator and tells the reader about a particular experience he had when he was fifteen years old. Additionally, during this passage, the only character is the narrator as other characters are not mentioned.
Considering this, to include dialogue in this passage or change all the content into a dialogue it is necessary to include more characters, as only if there are more characters involved there can be a conversation and interaction between them and this can serve to tell the events using dialogue. Therefore, the aspect that needs to be changed is that more characters would have to appear.