‘Date when continuous employment starts and the basis for calculating…

The correct answer is Option (4) → contract of employment

Option (1) letter of appointment — Incorrect. A letter of appointment carries the date by which the appointee must report on duty.

Option (2) attestation form — Incorrect. An attestation form carries personal details of the candidate, attested by him or her.

Option (3) job description — Incorrect. A job description is written while estimating manpower requirements, before recruitment starts.

Option (4) contract of employment — Correct. After the candidate accepts the offer, a written contract of employment is prepared. This date and the basis for calculating service are among its typical headings.