Возможный ответ:
Now, I'm going to give a talk about a healthy lifestyle.
To begin with, doing sport is an important part of everyone's life, especially for modern teenagers. I believe that sport helps us to stay healthy and strong. It also makes our body fit and improves our mood.
Besides, regular physical activity helps teenagers to reduce stress after long school days. As far as I know, many young people also go to the gym or do morning exercises at home.
To tell the truth, some of my friends prefer cycling or walking a lot instead of doing professional sport. Eating healthy food and drinking enough water is also very popular among teenagers nowadays.
However, in my free time I don't always do sport. I enjoy playing basketball with my classmates after school. I think that doing sports activities is really cool and necessary. In conclusion, I'd like to say that sport is not only about winning competitions, but also about having fun and being healthy.
That's all I wanted to say about healthy lifestyle.