Select from the following.
(1). Calcium carbonate
(2). evaporation
(3). circulatory systems
(4). sugar
(5). chlorine bleach
(6). one celled organisms
(7). glass
(8). cyanide

You are presented with the quiz "What removes harmful substances from water 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 "chlorine bleach is ideal for treating water". So, what's the best answer to the question?
Answer:
(5).