You are presented with the question "What do mollusks contain?" and the following answer choices: 
- harmful substances
 - Organic compounds
 - bacon
 - cayenne
 - acetic acid
 - dogs
 - Chlorophyll
 - Calcium carbonate

Now knowing that most mollusks have shells and coral reefs and shells are made of calcium carbonate, choose the best answer.


 

        Calcium carbonate 