The key answer of exercise 23

If you are studying for a test or an exam, it's important to do it healthily. First, it's very important to eat properly. Eat three good meals a day and don't snack while you are studying. Snacks must be healthy, fruit for example. Don't sit in front of a computer screen for more than an hour. If you do this, you'll damage your eyes. Take a ten minute break and rest your eyes. Look out of a window or close them. Stretch slowly to help your muscles. And get enough sleep. It's essential, if you want to study successfully.