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Answer 3 out of 4 questions correctly.

Carbon is one of the most abundant elements in the universe. It is formed in stars and found in a variety of celestial objects, including planets. Carbon is present in all of Earth's spheres and is an essential element for all living things.

A crater in the desert is shaped like a bowl and has large cliffs.

Meteor Crater in Winslow, Arizona

Scientists think most of Earth's carbon came from carbon-rich interstellar dust, comets, or asteroids that collided with Earth billions of years ago, early in its history. Today, so few carbon atoms are exchanged between Earth and space that Earth is considered a closed system. In other words, Earth does not gain or lose a significant amount of carbon from year to year.

However, Earth's carbon does not remain in one place. It continually moves between Earth's geosphere, hydrosphere, atmosphere, and biosphere, so the amount of carbon in each sphere changes from year to year.

Complete the sentences.