deforestation[森林砍伐] VS. afforestation[绿化/植树造林]

　　-eg: The main cause of soil erosion is deforestation for farmland reclamation.;

　　desertification[沙漠化];

　　renewable[可再生的];

　　pose a threat to[构成威胁]

　　-radiation poses a theat to people's health。