Hi Dicas,
I'm guessing the questionnaire activity you're working with is a Cuestionario (mod_quiz), just to be sure.
If you want to explain the 'why of correct or incorrect' to your students for all answer options in multiple choice questions, I'd recommend using the General feedback bit for each question, as this is a less cluttery way of showing feedback than when you'd have all the specific answer feedback in the blue question/answer box. I expect students would have trouble reading the jumble of question text, answer options and specific feedback for each answer if it's not so structured.
I'm guessing the questionnaire activity you're working with is a Cuestionario (mod_quiz), just to be sure.
If you want to explain the 'why of correct or incorrect' to your students for all answer options in multiple choice questions, I'd recommend using the General feedback bit for each question, as this is a less cluttery way of showing feedback than when you'd have all the specific answer feedback in the blue question/answer box. I expect students would have trouble reading the jumble of question text, answer options and specific feedback for each answer if it's not so structured.