Under the FIDIC Red Book (edition 1999), as part of the Contractor submission of Statement,...

Under FIDIC Red Book 1999, retention is calculated as a percentage (stated in Appendix to Tender) of the value of Works executed and Plant and Materials in accordance with Sub-Clause 14.5 that are on or off Site but intended for incorporation.

Option A is correct: Retention applies to the value of executed works.

Option D is correct: It also applies to Plant and Materials under Sub-Clause 14.5.

Option B is incorrect; advance payments and repayments are not part of retention calculations.

Option C is incorrect; changes due to legislation or costs are not included in retention calculation.