Forests are very important because they provide us with fresh air and food.
句意：森林非常重要,因为它们为我们提供了新鲜空气和食物.对划线部分提问划线because they provide us with fresh air and food我要的是划线提问，亲提问：Why are forests very important?为什么森林很重要？解释：对原因提问，用why。