Step 1: Understanding Section 106.
Section 106 of the Evidence Act states that when any fact is especially within the knowledge of any person, the burden of proving that fact is upon him.
Step 2: Applicability.
This section is applicable to:
- Parties to the suit.
- Strangers to the suit.
- Persons not parties but interested in the outcome of the suit.
Step 3: Conclusion.
Thus, the correct answer is (d) all of the above.