Which statement about proto-oncogenes is false?
◦ Many proto-oncogenes code for growth factors.
◦ A mutation must occur in a cell's DNA for a proto-oncogene to become an oncogene.
◦ If a proto-oncogene's gene product is produced in smaller quantities, a cell may become cancerous.
◦ Proto-oncogenes are normal genes with the potential to become oncogenes.