Instructions: 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").
Input: Fact1: contact between rocks over long periods of time causes rocks to smooth, Fact2: Primary rock types are Sandstone, and Shale., Question: what smooths over long periods of time due to contact? (A) oxygen (B) calcite (C) h2o (D) clouds (E) erosion (F) shale (G) bamboo (H) rivers
Output:
F