sentences: resources need to be managed & an example of managing / maintaining the number / the use of something is replacing that something ->  an example of managing the use of a resource is replacing that resource  an example of managing the use of a resource is replacing that resource & trees are a kind of natural resource ->  an example of managing the use of trees is replacing trees  an example of managing the use of trees is replacing trees & a tree can be replaced by planting a new tree each time one is cut down -> an example of managing the use of trees is planting a new tree each time one is cut down