The correct response is Establish ownership. To implement a classification scheme, you must perform seven major steps, or phases: 1. Identify the custodian, and define their responsibilities. 2. Specify the evaluation criteria of how the information will be classified and labeled. 3. Classify and label each resource. (The owner conducts this step, but a supervisor should review it.) 4. Document any exceptions to the classification policy that are discovered, and integrate them into the evaluation criteria. 5. Select the security controls that will be applied to each classification level to provide the necessary level of protection. 6. Specify the procedures for declassifying resources and the procedures for transferring custody of a resource to an external entity. 7. Create an enterprise-wide awareness program to instruct all personnel about the classification system.

References: Stewart, J. M., Chapple, M., & Gibson, D. (2015). CISSP: Certified Information Systems Security Professional Study Guide.

Edit: The Data Owner and Data Custodian are two different titles -- Shouldn't the answer be "Establish custodian"?