Final answer:
OCI Object Storage's Object Lifecycle Management feature can be used to set rules that automatically delete previous object versions after a set period, such as 120 days in the given scenario.
Step-by-step explanation:
The feature in OCI Object Storage that can be used to automatically delete previous object versions 120 days after they transition from the latest version to a previous version is called Object Lifecycle Management. With lifecycle management policies, you can set rules to automatically perform actions on objects within a bucket. For this scenario, you would create a rule to expire objects after they have been noncurrent for 120 days. These policies help in managing storage costs and ensuring compliance with data retention policies.