You are presented with the quiz "What does treating water remove before drinking it?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "treating water is used to remove harmful substances before drinking" and "ordinary tap water can be full of harmful substances like chlorine, pesticides and heavy metals". 

So, what's the best answer to the question?


 

    chlorine, pesticides, heavy metals       