In SAP S/4HANA Transportation Management, business partners (e.g., carriers, shippers) can be automatically assigned to documents using specific configuration settings. According to the SAP documentation:

Partner function (A): Partner functions define roles (e.g., carrier, ordering party) and can be configured with determination rules to automatically assign business partners based on criteria like location or agreement.

Freight order type (B): The freight order type can include a partner determination profile that specifies rules for automatically assigning business partners, such as carriers, to the freight order.

The other options are incorrect:

Freight unit type (C)controls freight unit creation but does not directly handle business partner assignment.

Business function (D)is a system-level setting for enabling features, not for partner assignment.