Not all of the changes created by technology are good. Advances in medical technology have extended the time people live.But sometimes the quality of life for these people is very low.For example,people can be kept alive by machines,even though they are permanently unconscious-in a coma. Technology has also led to the development of modern machines,such as cars,Cars allow us to mobile and travel freely,but they also create pollution and contribute to congestion in cities.Another machine,the air-conditioner,provides cool comfort but uses electricity;and the Freon chemical released during its use harms the environment.