Here's why:
* Linking verbs connect the subject of the sentence (Susan) to a word or phrase that describes or renames the subject (confident).
* In this case, "appeared" links Susan to the state of being "confident."
Think of it this way:
* The sentence is essentially saying "Susan was confident during the debate."
* The word "confident" acts as a predicate adjective, describing Susan.
Let me know if you have any other sentences you'd like to analyze!