sentences: plastic is a kind of material made by humans & a plastic spoon is made of plastic ->  a plastic spoon is made of a material that is made by humans  natural means grown in nature & made by humans / artificial is the opposite of natural ->  if something is made by humans then that something is not grown in nature  a plastic spoon is made of a material that is made by humans & if something is made by humans then that something is not grown in nature -> a plastic spoon is made of material that is not grown in nature