Explanation:

- Discharge by Notice

- Generally, a surety cannot unilaterally discharge his liability just by giving notice.

- Exceptions might occur where a termination is contractually allowed.

- Discharge by Novation

- When there is a mutual agreement to replace the old contract with a new one.

- This can discharge the surety's obligations.

- Discharge by Death

- A surety's death does not automatically discharge his liability.

- The estate might still be liable for obligations prior to the death.

- All the Above

- The surety can be discharged through these ways, but specific conditions apply.

All the Above (Option 4)

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