Fact 1: Erosion causes a river to become deeper and wider. Fact 2: Canyon formed as a consequence of river erosion. Given the two facts above, what are canyons formed by?

Select from: (A). rocks. (B). rainfall. (C). rivers. (D). mechanical force. (E). calcite. (F). silt. (G). water. (H). gravity.
Answer:
(C).