从方框中选择合适的词或短语,并用其正确形式完成短文. pleasant, collect, protect, some, take care of, try one's best, as soon as, cut down, pick up, visit One day I 1._______ one of my friends in a big town. Suddenly, a piece of beautiful music came to my ears. My friend's father quickly 2._______ some bags of litter and went outside. I aske d my friend, 'What's going on?' My friend said that there was a truck 3._______ litter outside. 'Whenever someone throws some l itter in, it gives out beautiful music. 4._______ other people hear it, they'll go out with their litter and throw it in.' 'It's a 5._______ way to help keep our city clean,' said my friend. 6._______ our environment is very important. Wherever you live, you can do something around your neighbourhood. Have you ever thrown 7._______ litter onto the ground? Have you ever drawn pictures on public walls?   Have you ever spat in public? Have you ever 8. _______ trees? If your answers are 'No', it means that you have already helped 9. ________ our environ ment. It is our duty to keep our environment clean and tidy. If everyone 10._______ to protect the environment, the world will become much more beautiful.