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: a cactus stem is used for storing water, Fact2: H2O is the scientific name for water., Question: what can a cactus stem store? (A) hydrogen (B) CO2 (C) h2o (D) H20 (E) O2 (F) liquid gold (G) thorns (H) rain
A:
C