Step 1: Determine Retiring Partner's Entitlements.
A partner upon retirement is due: - Profit share up to retirement date. - Goodwill share. - Share of accumulated profits and reserves. - Share of any gain or loss from asset/liability revaluation.
Step 2: Evaluate Options.
(A) Included.
(B) Included.
(C) Included.
(D) Included.
Step 3: Final Determination.
These four elements collectively constitute the amount payable to a retiring partner.
Final Answer: \[\boxed{\text{(A), (B), (C) and (D)}}\]