In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").
Q: Fact1: treating water is used to remove harmful substances before drinking, Fact2: Arsenic, a naturally occurring substance, contaminates water sources in many countries., Question: What is treating water used to remove before drinking? (A) arsenic (B) air (C) cellulose (D) chemicals (E) Collagen (F) loose dirt (G) water vapor (H) ice
A:
A