1. If you had worn protective clothing while volcano surfing , you __________ (not hurt) yourself.

Тип условного предложения - Conditional 3. Необходимо поставить глагол в Past Perfect.

If + Past Perfect, would have + Past Participle

В данном случае, необходимо образовать отрицательную форму would not have + Past Participle от глагола hurt. Все три формы глагола hurt совпадают: hurt - hurt - hurt

Получаем: wouldn't have hurt

Итоговое предложение:

If you had worn protective clothing while volcano surfing, you wouldn't have hurt yourself.

Ответ: wouldn't have hurt