Respuesta :
Answer: C. (Incurable)
Explanation: Incorrigible means beyond reforms, cannot change or be improved upon. When you say someone has incorrigible behavior, you are simply saying that the person's behavior is bad beyond correction or reform. You have tried all you can to correct that behavior yet the person cannot stop behaving in that way. In the question, he can't be cured of that bad thing they do. He is Incurable.
The word incorrigible in this sentence means: C. Incurable.
An incorrigible person is a hardened person who refuses to be changed or reformed. It is similar in meaning to the word, incurable because it describes a state of not being easily changed.
So, when the boy's sister was puzzled by his incorrigible behavior, it meant that his behavior was incurable.
Learn more about the word incorrigible here:
https://brainly.com/question/8517435