Q: Fact 1: Treating water is used to remove harmful substances before drinking. Fact 2: Arsenic, a naturally occurring substance, contaminates water sources in many countries. Given the two facts above, what is treating water used to remove before drinking?

Options are:
a). arsenic;
b). air;
c). cellulose;
d). chemicals;
e). Collagen;
f). loose dirt;
g). water vapor;
h). ice;
The answer is:
a).