pollution 1(无字幕).mp4 1)__________ is a big problem. Many places on 2) __________ are not clean. There is 3) __________ on the land and in the water. The air is 4) __________, too. People, cars, 5) __________ and many other things 6) __________ our world. How can you help? You can help keep our air 7) __________. Walk, 8) __________ a bike, or take a bus. Always put your trash in a trash 2) __________. Look for trash on the ground and 10) __________ it up. Help keep our land clean.