Choice "B" is correct. If the deviation rate in the auditor's sample is higher than the tolerable rate, the auditor will assess control risk as unacceptably high. If it turns out that the deviation rate in the population is less than the tolerable rate, the auditor will have made an improper decision by assessing control risk higher than appropriate.
Choice "c" is incorrect. If the deviation rate in the auditor's sample is less than the tolerable rate, the auditor will assess control risk as acceptably low. If it turns out that the deviation rate in the population exceeds the tolerable rate, the auditor will have made an improper decision by assessing control risk lower than appropriate.
Choice "d" is incorrect. When both the deviation rate in the auditor's sample and the deviation rate in the population exceed the tolerable rate, there will be no sampling error and the auditor will assess risk properly.
Choice "a" is incorrect. When both the deviation rate in the auditor's sample and the deviation rate in the population are less than the tolerable rate, there will be no sampling error and the auditor will assess risk properly.