This is a test of commonsense. Complete the next sentence:

How to prevent brain cancer
Be aware of your risk.
Doctors do not know what causes brain cancer in most cases, but there are certain factors that can increase your risk. Knowing these factors can help you identify your risk and potential symptoms, and get regular checkups.
The main risk factors for brain cancer include age, exposure to radiation, a family history of brain tumors, and currently having cancer that could metastasize (spread) to your brain from another area of your body. The brain, like the liver and lungs, has a lot of blood vessels.