With respect to the wbs numbering system, which of the following statements is true? a. the numbering system is a unique identifier known as the code of accounts, which is used to track the costs of the wbs elements. b. the numbering system is a unique identifier known as the code of accounts, which is used to track time and resource assignments for individual work elements. c. the numbering system is a unique identifier known as the wbs dictionary, which is used to assign quality control codes to the individual work elements. d. the numbering system is a unique identifier known as the wbs dictionary, which is used to track the descriptions of individual work elements.