At what time is the air the freshest in the day?The air is never as fresh as ear

Early rising is helpful in more than one way. First, it helps to keep us fit. We all need fresh air. But air is never as fresh as early in the morning. Besides, we can do good to our health from doing morning exercise. Secondly ,early rising helps us in our studies. We learn more quickly in the morning, and find it easier to remember what we learn in the morning. Thirdly, early rising enables us to plan the work of the day. We cannot work well without a good plan. Just as the plan for the year should be made in the spring, so the plan for the day should be made in the morning. Fourthly, early rising gives US enough time to get ready for our work, such as to wash our faces and hands and eat our breakfast properly.
Q11．At what time is the air the freshest in the day?
12.Why do early rising help US in our study?
13.How can we work well according to the author?
14.What should we prepare before our work?
15.What is the main idea of this passage?