Explanation:

- The sentence talks about soldiers leaving an indelible impression, which means the impression cannot be removed or forgotten.

- Option 1: Permanent

- This means lasting or intended to last indefinitely without change.

- This matches the meaning of "indelible".

- Option 2: Fleeting

- This means lasting for a very short time.

- This does not match "indelible".

- Option 3: Hilarious

- This means extremely amusing.

- This is unrelated to "indelible".

- Option 4: Eradicable

- This means able to be removed or destroyed completely.

- This is the opposite of "indelible".