Assertion: cave's opening | /r/HasProperty | natural
Facets:
Source sentences:
text: A cave is a natural opening in the ground extending beyond the zone of light and large enough to permit the entry of man.
text: Caves are natural openings in the Earth that are large enough to allow a person to enter and extend beyond the zone of light penetration.
text: Ruby Falls Cave, unlike Lookout Mountain Cave, had no natural openings and could not be entered until the 20th century; it therefore does not have the various artifacts which are often associated with caves in the southeastern United States.