Final answer:
The beneficiary signature is required for any change to the beneficiary in a revocable beneficiary designation.
Step-by-step explanation:
The correct answer is d) Revocable beneficiary. A revocable beneficiary is a person or entity named to receive benefits from an insurance policy, retirement plan, or other investment account. The beneficiary's signature is required to make any changes to the beneficiary designation.
For example, let's say John names his sister Jane as the revocable beneficiary of his life insurance policy. If John wants to change the beneficiary to his daughter Sarah, he would need Jane's signature to complete the change.