Voyageurs, Cedar Breaks, Guadalupe Mountains, Congaree, North Cascades, Grand Staircase-Escalante, Isle Royale, Grand Canyon, Wrangell-St. Elias, Great Sand Dunes
The solar system came into being about 4.5 billion years ago when a cloud of interstellar gas and dust collapsed resulting in a solar _____ , a swirling disk of material that collided to form the solar system.
In the Rocky Mountains beaver dams slowly filter billions of tons of water. The ponds build up soil and _____s and help prevent floods and droughts.
Digits make up numerals and numerals stand for an idea of a _____ just like letters make up words and words stand for ideas.