Detailed 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").
Q: Fact1: damming a river can cause a lake to form, Fact2: Nothing alters a river as totally as a dam., Question: What can a dam form? (A) fens (B) rain (C) lake (D) water (E) cracks (F) H2O (G) valley (H) canyon
A:
C