sentences: if something is required to create something else then that something is needed to make that something else & creating paper requires cutting down trees ->  cut trees are needed to make paper  cut trees are needed to make paper & trees are a kind of natural resource ->  cut trees are a kind of resource that is needed to make paper  cut trees are a kind of resource that is needed to make paper & recycling reduces the resources needed to make something -> recycling paper reduces the cutting of trees