Which Is a Plausible Explanation for the Presence of Carbon

Multiple Choice

Which is a plausible explanation for the presence of carbon dioxide in Earth's early atmosphere?

A) Volcanic eruptions could have released carbon dioxide into the atmosphere.
B) Cyanobacteria were present on Earth 3.5 billion years ago.
C) Retroviruses could have catalyzed the formation of carbon dioxide.
D) Geysers may have produced Earth's early environment.
E) Chemical reactions with water would have resulted in the formation of carbon dioxide.