natural ability; natural action; natural childbirth; natural covering; natural depression; natural elevation; natural enclosure; natural endowment; natural event; natural family planning; natural fiber; natural fibre; natural gas; natural glass; natural history; natural immunity; natural language; natural language processing; natural language processing application; natural language processor; natural law; natural logarithm; natural number; natural object; natural order; natural phenomenon; natural philosophy; natural process; natural resin; natural resource; natural resources; natural rubber; natural science; natural scientist; natural selection; natural shape; natural spring; natural state; natural theology; natural virtue;