Explanation
Defining control requirements is the next step to ensure the security policy framework encompasses the new business model because it is a process of identifying and specifying the security measures and standards that are needed to protect the data and applications accessed by the BYOD devices. Defining control requirements helps to establish the baseline security level and expectations for the BYOD strategy, as well as to align them with the business objectives and risks. Therefore, defining control requirements is the correct answer.
References:
https://www.digitalguardian.com/blog/ultimate-guide-byod-security-overcoming-challenges-creating-effec
https://learn.microsoft.com/en-us/mem/intune/fundamentals/byod-technology-decisions