Shopping cart approval levels in SAP SRM are determined by three key characteristics: T-class (transaction class), Plant, and Value. The T-class defines the transaction type (e.g., direct material, indirect material), the Plant represents the organizational unit, and the Value determines the monetary threshold for approval workflows. Options A and B incorrectly include company code or purchase group instead of T-class, while D includes purchase group which is not a determining factor for approval levels.