What is an example of a natural disaster threat?

A tornado that demolished two city blocks including condominiums is the clearest example of a natural disaster threat among the options provided. Natural disasters are events caused by natural forces — such as tornadoes, hurricanes, earthquakes, floods, and wildfires — rather than by human action or industrial failure. A tornado is an atmospheric phenomenon entirely outside human control, making it a prototypical natural hazard. An aircraft incident is classified as a technological or man-made disaster, as it involves failure of human-engineered equipment or human error. Workplace violence is a human-perpetrated event and falls under the category of human-caused or intentional disasters. Ground instability causing a sinkhole that collapses school wings is a more nuanced scenario; sinkholes can be natural or human-induced (e.g., from mining or infrastructure failure), but without additional context it is more often classified as a geological or technological hazard rather than a straightforward natural disaster. The tornado option is unambiguous and is the standard textbook example of a natural disaster, making it the best answer here.