Explanation:

- Ancient: Customs often have a historical origin, tracing back through generations, adding deep-rooted significance and stability to societal practices.

- Invariable and Continuous: Customs are expected to be consistent and uninterrupted over time, which ensures their acceptance and recognition within a community.

- Reasonable: For a custom to be valid, it must be logical and fair, aligning with the moral and social standards of the society it serves.

- All of the above: Each of these elements is crucial to the essence of a genuine custom, making them collectively indispensable.

- Answer: Option 4 - All of the above