I think she is making speculation due to the sadden change of behavior.
<span>C. Youthful
"Child-like" as a word can best be replaced by the adjective youthful. It is the correct part of speech to fit into the rest of the sentence, and it means basically the same thing. Acting like a child is acting as one did in youth, so youthful and child-like are very close synonyms. </span>
The bolded pronoun in the given sentence is the word "which". This pronoun is an example of an interrogative pronoun. Interrogative pronouns are pronouns that are used to introduce a question. The antecedents of interrogative pronouns are unknown because it is what is being asked in the sentence that is missing.
Clauses highly improve sentence structures. They can make the sentence sound a lot better to the tongue, and it even make the sentence easier to understand. I hope this helps! :)
