Final answer:
If a graduate nurse does not have the required Authorization to Test (ATT) form, they will likely not be allowed to take the exam at the testing center.
Step-by-step explanation:
If a graduate nurse arrives at the testing center without the required Authorization to Test (ATT) form, the likely course of action is b) The testing center staff would not allow him to test without his ATT. The ATT is a crucial component for the identification and authorization process, and without it, testing centers usually have strict policies that would prevent the candidate from taking the exam. Testing centers require the ATT as it confirms that the candidate has met all necessary eligibility requirements and is authorized by the nursing regulatory body to take the exam.