The Rocky Mountains of North America Were Formed By

The Rocky Mountains of North America were formed by:

A) an ancient, mid-oceanic volcanic ridge now uplifted to become dry land.
B) folding of Earth's crust where two crustal plates collided along a subduction zone.
C) asteroid impacts during the first billion years of Earth's history.
D) shrinking and folding of Earth's crust as Earth cooled and contracted.