Shihab and Kaniz are walking to school along the river. At one place, they stop to see somethings. Some people are bathing in the river. Some are washing their clothes. A man throws some rubbish into the river. Shihab and Kaniz become upset. They request the man, "Please, don't throw the rubbish into the river. It'pollutes the water."

Shihab and Kaniz also see some polythene bags, plastics bottles and some other things floating on the river. They start talking about it.

Kaniz : Look, Shihab, the water is so dirty!
Shihab : Yes, Kaniz. We can't bathe in this polluted water.
Kaniz : Fishes also can't swim easily.
Shihab : Yes. Sometimes, the fish gets caught into polythene bags. It puts them in danger.
Kaniz : You are right. We should save them.
Shihab : Sure. We must keep the water clean.
Kaniz : and Shihab reach their school and share this story with their friends. They discuss how to keep the water clean and safe.

Choose the best answer from the following alternatives and write them in your answer script.