You are presented with the question "what is in limestone?" and the following answer choices: 
- abrasion
 - fossils
 - an anion
 - acid
 - nitrogen
 - gypsum
 - carbon
 - NaCl

Now knowing that carbon may be stored in sedimentary rock for millions of years and limestone is a rock composed of calcium, carbon and oxygen, choose the best answer.


 

       carbon  