Fact 1: Cells are the microscopic building blocks of organisms.

Fact 2: Coral reefs are limestone formations composed of tiny sea organisms and their remains.

Given the two facts above, answer the question "The microscopic building blocks of coral reefs are" with the following options: 
- limes
 - porous
 - complex
 - made
 - electrons
 - cells
 - white
 - helium atoms


 

      cells   