Given the task definition and input, reply with output. 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").

Fact1: stalactites are formed by deposition, Fact2: Stalactites and stalagmites are common speleothems., Question: What are speleothems formed by? (A) calcite (B) craters (C) deposition (D) tornadoes (E) deuterostomes (F) tiny polyps (G) haploid plants (H) hurricanes
C