You are presented with the question "The microscopic building blocks of coral reefs are" and the following answer choices: 
- limes
 - porous
 - complex
 - made
 - electrons
 - cells
 - white
 - helium atoms

Now knowing that cells are the microscopic building blocks of organisms and coral reefs are limestone formations composed of tiny sea organisms and their remains, choose the best answer.


 

      cells   