What type of tie-off is made just inside the entrance for backup purposes?

The correct answer is secondary tie-off, which plays a crucial role in ensuring diver safety within cavern environments. A secondary tie-off is established just inside the entrance of the cave or cavern to serve as a backup attachment point for the diver's guideline. This is essential because it provides redundancy; if the primary tie-off were to fail or become dislodged during the dive, the secondary tie-off ensures that divers still have a reliable point to guide them to the exit.

Establishing a secondary tie-off adds an additional layer of safety by creating a backup plan for navigation and means of escape if needed. This is particularly important in cavern diving, where visibility can decrease rapidly, and a clear path to the exit is vital for preventing disorientation. Thus, secondary tie-offs are considered best practice for safety in cavern diving, allowing divers to maintain their orientation and safety in potentially hazardous environments.