Choice "B" is correct. The auditor may be able to reduce the required sample size by separating items subject to sampling into relatively homogenous groups on the basis of some characteristic related to the specific audit objective.
Choice "a" is incorrect. While PPS sampling results in a stratified sample, it is a result of the sampling method employed and does not require the auditor to perform stratification since it occurs automatically.
Choice "d" is incorrect. The estimated tolerable misstatement does not affect the decision to stratify.
Choice "c" is incorrect. The standard deviation of the recorded amounts represents the population's variability. Therefore, the auditor would be most likely to stratify when the standard deviation is high, not low.