Explanation:

- Prior Interest: This is an interest that is established before a specified event, such as the birth of an unborn person. It's necessary to have a prior interest to allow for a subsequent interest to be created.

- Subsequent Interest: This is an interest that will come into play after a prior interest has been established. It typically benefits someone upon the occurrence of a future event.

- Equal Interest: This implies equal benefits or rights to all parties involved and doesn’t specifically prioritize any unborn person.

- None: Suggests that no interests are needed in advance, which is not applicable when assigning benefits to someone unborn.