Option B is correct: The Contractor must obtain approval from the Engineer/Employer before making design changes.
Option C is correct: The Contractor can submit Value Engineering proposals to improve efficiency or reduce costs.
Option A is incorrect; unilateral changes are not allowed.
Option D is incorrect; Value Engineering can be proposed even after initial submission.
References:
FIDIC Yellow and Silver Books 1999 Edition, Sub-Clauses 4.1 and 4.4
FIDIC Contract Manager Study Guide, Module on Design and Value Engineering

According to FIDIC Red Book 1999, Sub-Clause 14.2, the Advance Payment Guarantee must be a bank guarantee issued by a reputable bank acceptable to the Employer. This bank guarantee serves as security to ensure that the advance payment made by the Employer will be repaid if the Contractor fails to fulfill contractual obligations. The bank guarantee is a commonly used, reliable instrument providing direct financial assurance to the Employer.
Other instruments like surety bonds or parent company guarantees may be acceptable only if explicitly agreed, but the standard requirement is a bank guarantee.
Declaration of joint and several liability is not a typical form of guarantee for advance payments.
References:
FIDIC Red Book 1999 Edition, Sub-Clause 14.2 - Advance Payment Guarantee FIDIC Contract Manager Study Guide, Module on Payment Procedures and Guarantees

Under FIDIC Red Book (1999), the Value Engineering Clause requires the Contractor to notify the Engineer with full details and cost implications when proposing Value Engineering changes. The Engineer then follows the Variation procedure in Sub-Clause 3.5 to agree or determine the cost adjustment, which will be reflected in the Contract Price.
This ensures transparent handling of Value Engineering proposals and proper contractual adjustments.
References:
FIDIC Red Book 1999 Edition, Sub-Clause 13.1 - Value Engineering
FIDIC Contract Manager Study Guide, Module on Variations and Value Engineering

Comprehensive and Detailed Explanation:
Option A is NOT a Variation because it originates from a Value Engineering proposal by the Contractor, not from Employer or Engineer instruction or request.
Options B, C, and D are all variations initiated by the Employer or Engineer.
References:
FIDIC Red Book 1999 Edition, Clause 3 - Variations
FIDIC Contract Manager Study Guide, Module on Variations

Under the FIDIC Red Book (1999), the Tender Documents typically include:
The Bill of Quantities (Option B), which provides detailed quantities for priced items and forms a basis for tender pricing.
The Specifications (Option E), which define the technical requirements for the Works.
The Schedule of Guarantees (Option A) is usually provided later, during contract formation, not as part of tender documents.
Employer's Requirements (Option C) are more commonly referenced in design-build contracts such as the Yellow Book, not the Red Book which is traditionally a design-bid-build contract.
Schedule of Baselines (Option D) is not a standard tender document in FIDIC Red Book contracts.
References:
FIDIC Red Book 1999 Edition - Tender Documents Section
FIDIC Contract Manager Study Guide, Module on Tendering Documents