Which of the following has PRIMARY responsibility to define the requirements for IT service levels...

 The business manager has the primary responsibility to define the requirements for IT service levels for the enterprise, as they are the ones who understand the business needs, objectives, and expectations from the IT services. The business manager should communicate these requirements to the IT service provider, who should then design, deliver, and monitor the IT services according to the agreed service levels. The help desk, the CIO, and the business continuity vendor are not primarily responsible for defining the IT service level requirements, although they may have roles in supporting, implementing, or ensuring them. References := CGEIT Review Manual, 27th Edition, Domain 1: Governance of Enterprise IT, page 20-21.