It is an unfortunate fact of today's life that most people are growing up unable to see the stars. The prime night sky exists only in pictures. This is true not only in cities and suburbs, but also in rural areas. We have lost our view of the _____1_____ and dirtied our nighttime environment as well.Such a loss might be acceptable if light pollution were the inevitable price of progress , as it is not. Most sky glow is unnecessary. It _____2_____ mainly from lighting sources that do little to increase nighttime safety，security or utility. They produce only glare, _____3_____ over one billion dollars annually in the U. S. alone.For science, the impact has been even more dramatic. _____4_____ require observations of extremely faint objects that can only be made with advanced devices at sites free of air pollution and urban sky glow. For example, some images of the objects can offer information about faraway corners of the universe, _____5_____ us understand the way in which our world was actually formed, yet the light from these objects can be lost at the very end of its journey in the glare of our own sky.Reducing light pollution is not _____6_____. It _____7_____ that public officials and citizens be aware of the problem and act to counter it. As individuals, people can help _____8_____ sky glow just by using lighting only, when necessary.The stars above us are a _____9_____ heritage. We must _____10_____ our best to preserve it.[A] priceless [B] stars [C] helping [D] coming [E] requires [F] comes [G] science[H] scientists [I] did [J] do [K] easy [L] costing [M] reducing [N] difficult [O] reduce