How does the presence of an oncogene lead to the formation of a tumor

it becomes a horrible gene that can become permanently turned on or activated when it is not supposed to be.

Explanation:

this is because the cells get out of control and can lead to cancer

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.