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A is corrent because tests of controls are only performed on controls that the auditor plans to consider is assessing the risk of material misstatement. Performance of tests of controls on these controls may reduce the scope of substantive procedures needed.
B is incorrect because even though some controls have a material effect upon financial statement balances, they may not be relied upon if substantive testing may be more efficient.
C is incorrect because the auditor is unlikely to test controls in which reportable conditions exist since they cannot be relied upon.
D is incorrect because the decision of whether or not to perform tests of controls is determined by employing professional judgment based upon the results of assessing control risk, not by a random sample.