Q: You are presented with the quiz "What is treating water used to remove before drinking?" 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 "arsenic, a naturally occurring substance, contaminates water sources in many countries". So, what's the best answer to the question?

Available options: A. arsenic; B. air; C. cellulose; D. chemicals; E. Collagen; F. loose dirt; G. water vapor; H. ice;
The answer is:
A.