Final answer:
The correct word to complete the sentence is 'dry', as it contrasts caves with water features such as streams and lakes.
Step-by-step explanation:
Some caves are characterized by their varying conditions. While some caves may indeed be dry, others are known to have features such as underground streams and lakes. The correct word to fill in the blank of the given sentence is 'dry', as it is the opposite condition to containing water like underground streams and lakes. Cave environments can range from dry and inhabitable areas to others that are rich with water resources, illustrating the diverse ecosystems that can exist within these geological formations.