Explanation:

- Doctrine of Res Judicata: It's a legal principle in civil suits. It prevents the same dispute from being tried again once there's been a final judgment.

- Changing Circumstances:

- Situations that evolve over time.

- Not applicable to Res Judicata, as this focuses on settled matters.

- Static Situations:

- Remain the same without change.

- Res Judicata applies, as it deals with decisions that are not subject to alteration once decided.

- Both (a) and (b) above:

- Res Judicata specifically applies to settled cases, not changing circumstances.

- None of the above:

- Not correct, as Res Judicata certainly applies to settled, static situations.

- Correct Answer: Option 2 - Static situations