Fact 1: Cells that divide uncontrollably may form a tumor, or abnormal mass of cells.

Fact 2: Abnormal cells are irregular in shape.

Given the two facts above, answer the question "Cells that divide uncontrollably may form an irregular what?" with the following options: 
- Epidermis
 - massive damage
 - Veins and arteries.
 - permineralization
 - flow of electrons
 - mass of cells
 - illness
 - swamp vegetation


 

      mass of cells   