Explanation:

- The phrase "shocked at his ______ laughter" implies that the laughter was surprising in some way.

- Unrestrained: This option suggests that the laughter was wild or uncontrolled, which could indeed shock guests. It's a fitting choice for the sentence.

- Unrecognised: This suggests that the laughter was not identified or acknowledged, which doesn't match the context of shocking guests.

- Unresolved: This implies something is not settled or finished, not applicable to laughter itself.

- Unremarkable: This means ordinary or not worth noticing, which would not shock guests.