The oil is attacked by naturally occurring microbes which break it down.原油受到了自然产生的分解油类物质的微生物的侵蚀。The body produces chemicals called endorphins to control the pain.身体自然产生叫做内啡肽的化学物质来控制疼痛。Testosterone is a hormone that occurs naturally in the human body.睾丸激素是人体内自然产生的一种激素。