Ozone is a very active gas. When it is lower down in the atmosphere, it is closer to living things and can harm them. It can damage the leaves of plants and effect how they use sunlight to provide food. In humans it can cause headaches, eye irritation, coughs and chest discomfort.
If I've got it right, her target rate is <span>A. the heart rate she should maintain during most exercise to obtain fitness and health benefits. It's the most suitable one.</span>
