What are they doing? Why?

Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
   cleaning      dirty      doing      greener      picking up      watering   
People in the picture are a place. Some people are rubbish, bottles and plastic bags while some are trees and flowers. They are the clean-up activity because this makes the environment and makes the street less .