Rivers and mountains are examples of boundaries. a. intangible b. territory c. tangible d. sovereign
(it's not b)

The term boundary refers to a wide range of real and conceptual structures which denotes transitions between two adjacent habitats.

Rivers and mountains are examples of tangible boundaries. Correct C Tangible boundaries are boundaries that arise because of discontinuities between patches (a consequential boundary, such as a forest–field boundary), or they may cause discontinuities between patches (a causal boundary, such as a fence that encloses a herd of cattle).

brave new world, aldous huxley (1932)

polar areas, such as antarctica or the south pole.