Final answer:
Indirect characterization involves learning about a character through their speech, actions, thoughts, and other characters' reactions to them. Among the provided options, what the main character says and how other characters react to them are examples of indirect characterization, as can be thoughts, if not directly stated by the author.
Step-by-step explanation:
Characterization is a literary device authors use to present and develop characters within a story. Two types of characterization exist: direct and indirect characterization. Direct characterization is when the author explicitly describes a character. On the other hand, indirect characterization is when readers learn about characters through their speech, actions, appearance, thoughts, and how other characters interact with or react to them.
Among the options given, 'what the main character says' and 'how another character reacts to the main character' are examples of indirect characterization. The thoughts of the main character are also a form of indirect characterization if they are presented to the reader without direct statements from the author about what the character is like. However, 'a description of how the main character looks' is generally considered direct characterization unless it is inferred through the reactions or observations of other characters rather than stated outright by the narrator.