Choice "B" is correct. Tests of controls include such procedures as inspecting documentation, inquiry, observation, and reperformance. Note that inquiry alone is not sufficient as the auditor should use a combination of procedures.
Choice "a" is incorrect. Analytical procedures are used for planning purposes, as substantive tests, and as an overall final review, but they do not provide evidence about control risk.
Choice "c" is incorrect. Calculation is used as a substantive test rather than as a test of controls.
Choice "d" is incorrect. Confirmation represents a substantive test rather than a test of controls.