水中游动最快的旗鱼，速度可达108km/h；陆地上跑得最快的猎豹，1s可跑40m；空中飞行最快的褐海燕，每分钟能飞行5km，比较它们速度的大小(        )

   Teenagers live very busy lives and often forget to think about their diet and exercise. How much do you know about keeping healthy and fit?
   Healthy eating along with regular exercise is probably the only way to become fit. Diets are useless in the long term, about 20% of teenagers say they have tried eating less and skipping meals to control their weight. If you eat properly and exercise regularly, you will lose weight, keep fit and feel great.
   As a teenager, it is important to give your body energy it needs. If you skip meals, you don’t get enough energy, and then you feel tired. For a healthy diet, you should eat mostly rice, bread, vegetables and fruit.
   Exercise is something that can help to make you look good, feel good and be healthy. Teenagers should spend at least 30 minutes exercising, five times a week. It is easy to do! Walking and riding your bike to school, and doing some school sports. If you follow the suggestions above, you will look and feel much better!

目前世界上人口数最多的大洲是（　　）