Ответ:
Общий: Is the healthy diet very important for the preventing of many diseases?
Специальный: Why is the healthy diet very important for the preventing of many diseases?
Вопрос к подлежащему: What is very important for the preventing of many diseases?
Альтернативный: Is the healthy diet or doing sports very important for the preventing of many diseases?
Разделительный: The healthy diet is very important for the preventing of many diseases, isn't it?