Dust and particles of pollution from factories and industries worsen the effects of light pollution. If one city has a lot more light pollution than another， Ward says， that city will suffer the effects of light pollution on a much greater scale.

Hazy skies also make it far more difficult for astronomers to do their jobs.

Cities are getting larger. Suburbs are growing in once dark， rural areas. Light from all this new development is increasingly obscuring （使变模糊） the faint （微弱的） light given off by distant stars. And if scientists cant locate these objects， they cant learn more about them.

Light pollution doesnt only affect star visibility. It can harm wildlife too. Its clear that artificial light can attract animals， making them go off course. Theres increasing evidence， for example， that migrating （迁徙） birds use sunsets and sunrises to help find their way， says Sydney Gauthreaux Jr.， a scientist at Clemson University in South Carolina. When light occurs at night， he says， it has a very disruptive （破坏性的） influence. Sometimes birds fly into lighted towers， high-rises， and cables from radio and television towers. Experts estimate that millions of birds die this way every year.

31　On a clear night， people can see

A　150 stars.

B　hundreds of stars.

C　one thousand stars.

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