阅读下面短文，从短文后所给的四个选项中，选出可填入空白处的最佳选项．

　　One day I was visiting one of my friends in a big town． Suddenly 　　1　　 beautiful music came to my ears． My friend’s father quickly picked up　　 2　　 and went outside． I asked my friend，“　　 3　　 ？”My friend said that there was a truck　　 4　　 rubbish outside．

　　“ 　　5　　 someone throws in some rubbish，it gives out beautiful music． 　　6　　 other people hear it，they go out with their rubbish and 　　7　　”

　　“It is a　　 8　　 way to help keep our city clean．”said my friend．

　　　　9　　 our environment(环境) is very important． Wherever you　　 10　　 ，you can do something around your neighborhood．

　　Have you ever thrown any litter onto the ground? Have you ever draw pictures on　　 11　　 ? Have you ever spat　　 12　　 a public place? Have you ever cut down trees? If your answers are “　　 13　　 ”，it means that you have already helped protect our environment．

It is our duty to keep our environment　　 14　　 ． 　　15　　 everyone tries his best to protect(保护) the environment，the world will become much more beautiful．

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