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: most canyons are formed by flowing rivers through erosion over long periods of time, Fact2: The Columbia River Gorge is a spectacular river canyon cutting through the volcanic rock of the Cascade Mountain Range., Question: What was formed through erosion over long periods of time? (A) Columbia River Gorge (B) a hydraulic system (C) swamp vegetation (D) Mississippi River delta (E) the Moon (F) Calcium carbonate (G) the Himalayan mountains (H) permineralization
A