Final answer:
In auditing, the auditor must be alert for evidence that controls might be ineffective, even if only once or twice.
Step-by-step explanation:
When testing controls in an audit, option B is correct: the auditor must be alert for evidence that the control might be ineffective, even if only once or twice.
While it is important to gather evidence that a control is effective, it is equally crucial to look for any indications that the control might not be working as intended, even if it happens infrequently.
By doing so, the auditor can identify potential risks or weaknesses in the control environment and take appropriate measures to address them.