star；still；good；rest；up；how；pollution；stop；small；see；towards |
Look up at the sky at night.What can you see？Before electric lights，people could often see about 2，500 different stars.Now，light fills the skies over our cities.This is called light.Because of it，people in cities can often only see about ten!
Most of the time，light helps us.We canbecause of it.It gives plants energy.But light isn't always.We need times of dark.One hundred years ago，we had those times of dark.Now the night is like day.Some scientists are worried about this light effects（影响）our health.These scientists are studying the effects of light pollution.
Other scientists are finding ways tolight pollution and make our lives better.For example，many street lights now have covers.The covers focus the lightthe ground.They stop the light from goinginto the sky.They also save energy.The covers are achange，but they canhave a positive（正面的）effect.
