You are presented with the question "Brain tumors occur when what is no longer regulated?" and the following answer choices: 
- fossil fuels
 - headaches
 - voltage
 - heat or cold
 - cell cycles
 - critical organs
 - cerebellum
 - migraines

Now knowing that cancer is a disease that occurs when the cell cycle is no longer regulated and brain tumors are one of the fastest growing cancers today, choose the best answer.


 

     cell cycles    