Select the best answer from the choices list and then give an explanation:

Example:
Question: Is the following trait inherited or acquired?
NAME_1 has a scar on his left leg.
Choices: [0: 'inherited', 1: 'acquired']
Answer: 1 acquired
Explanation: Children do not inherit their parent's scars. Instead, scars are caused by the environment. People can get scars after they get hurt. So, having a scar is an acquired trait.

Your task:
Question: Select the elementary substance?
Choices: [0: 'methane (CH4)', 1: 'water (H2O)', 2: 'zinc (Zn)']
Answer: