A limitation is ______ the sun is not out; energy cannot be collected.

Plants, wind, and rain can help clean the (8) _________ to make it safe to breathe even if it came out of a car or a factory.

(7) _________ from our bathtubs and sinks can be cleaned at treatment facilities so it can be ready to drink.

Trees that are cut down can be replaced (6) _______when seeds or baby trees are planted.

Renewable resources are resources that can be replaced during a human __________.

Air, rocks, metals, _________, and salt are all natural resources.

A natural resource is a material found in (3) _________ that is used by living things.

Food, water, and sunlight are all examples of (2) ____________.