Choice "B" is correct. Observation and inspection may be used to evaluate the design of controls. Observation of entity personnel applying control activities is a procedure that would likely provide evidence about the design of the activities.
Choice "d" is incorrect. Reperforming control activities provides the auditor with evidence about the operating effectiveness of specific control activities, not the design effectiveness.
Choice "c" is incorrect. Analytical procedures would not provide the auditor with evidence about the design of specific control activities.
Choice "a" is incorrect. Vouching a sample of transactions directly related to control activities would not provide the auditor with evidence about the design of specific control activities.