Choice "C" is correct. The auditor should consider the tolerable rate of deviation from the control structure policies or procedures being tested, the likely rate of deviations, and the allowable risk of assessing control risk too low.
Choice "d" is incorrect. The risk of incorrect acceptance is relevant for substantive tests of details rather than tests of controls.
Choice "a" is incorrect. The nature and cause of the deviation is not considered in determining a sample size for tests of controls.
Choice "b" is incorrect. The population size is generally not considered in determining a sample size for tests of controls.