Fact 1: Oncogenes promote the division of cells with damaged DNA.

Fact 2: Carcinogenic or oncogenic effects cause cancer.

Given the two facts above, answer the question "Cells with damaged DNA are more likely to divide when exposed to what?" with the following options: 
- harmful substances
 - apoptotic genes
 - sulfur dioxide
 - a tumor suppressor
 - Electrical energy
 - heat or cold
 - immune system
 - a carcinogen


 

        a carcinogen 