You are presented with the quiz "Humans have collected and grown foods rich in what for thousands of years?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "humans have collected and grown mushrooms for food for thousands of years" and "foods rich in chlorine are mushrooms, parsley, sweet potato, rhubarb, and especially tomato". 

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


 

    chlorine       