Explanation:

- After the settlement of issues in a civil suit, parties are required to file the list of witnesses who may be called for examination.

- As per Order XVI, Rule 1 of the Code of Civil Procedure (CPC), 1908, the list of witnesses must be filed within 15 days from the date on which the issues are settled.

- This ensures timely progress of the trial and avoids unnecessary delays.

- Option:1, 15 days — This is the correct answer.

- Option:2, 30 days — This is not correct as CPC specifies 15 days.

- Option:3, 45 days — This period is incorrect according to the procedural law.

- Option:4, 60 days — This is a much longer period than allowed by law and is not correct.