In SAP S/4HANA, when managing component substitutions within a Bill of Material (BOM), the "Alternative Item Group" functionality is used. This feature provides specific strategies for material withdrawal in production. The two primary strategies are:

1. 100% check (Strategy 1): The system attempts to cover the total required quantity with a single component from the group. It checks the availability of the items sequentially based on their defined priority and usage probability until it finds one that can fulfill the entire requirement.

2. Manual maintenance (Strategy 2): Also known as "Manual selection," this strategy requires user intervention. During the goods issue or backflush process, the system presents the list of alternative components, and the user must manually select which item and quantity to consume.

A. First in first out (FIFO): This is an inventory valuation method or a stock removal strategy in warehouse management, not a BOM alternative item strategy.

B. Simultaneous: This is not a standard strategy for alternative item withdrawal in an SAP BOM. The system processes alternatives sequentially or via manual choice.

1. SAP S/4HANA Help Portal, "Alternative Items": This official documentation outlines the functionality of alternative item groups. It states, "You can define a strategy for withdrawing alternative items from stock... Strategy 1: The system tries to meet the material requirements with one material... Strategy 2: The user has to select the material during the backflush process." This directly supports "100% check" and "Manual maintenance/selection". (Path: SAP S/4HANA -> Product Assistance -> Enterprise Business Functions -> Logistics -> Production Planning and Control (PP) -> Basic Data (PP-BD) -> Bills of Material (BOMs) (PP-BD-BOM) -> Alternative Items).

2. SAP S/4HANA Help Portal, "Creating an Alternative Item Group": This document details the fields used to configure alternative items. For the "Strategy" field (technical name: AISTR), it specifies the available entries: '1' for a 100% check based on usage probability and '2' for manual selection. This confirms the two valid strategies. (Path: SAP S/4HANA -> Product Assistance -> ... -> Bills of Material (BOMs) (PP-BD-BOM) -> Alternative Items -> How to Create an Alternative Item Group).