Which of the following is an example of a speleothem?

Stalactites are indeed an example of a speleothem. Speleothems are mineral formations that occur in caves as a result of the deposition of minerals from dripping or flowing water. Stalactites specifically form from the dripping of mineral-rich water from the cave ceiling, where as the water evaporates, it leaves behind deposits of minerals, typically calcium carbonate. Over time, these deposits build up to create the icicle-shaped formations that hang from the ceiling.

Cave pearls are also a type of speleothem, formed from layers of minerals around a nucleus, but stalactites are more commonly referenced in the context of classic speleothem examples. Cave fish and cave spiders refer to living organisms adapted to life in dark cave environments and do not fall under the definition of a speleothem, which relates to mineral formations rather than biological entities.