You are presented with the question "What breaks up into two lighter elements when an animal divides into two parts?" and the following answer choices: 
- the blood cells
 - the heart
 - Energy.
 - the main element
 - heat energy
 - light energy
 - the nucleus
 - sensory neurons

Now knowing that fission takes place when an animal divides into two parts and if the nucleus breaks up into lighter elements, it is called fission , choose the best answer.


 

       the nucleus  