正解:C
The most useful information regarding an organization's risk appetite and tolerance is provided by its risk profile, as this is a document that summarizes the key risks that the organization faces, the potential impacts and likelihoods of those risks, and the acceptable levels of risk exposure for different objectives and activities.
A gap analysis is a tool that compares the current state and the desired state of a process or a system, and identifies the gaps that need to be addressed. Audit reports are documents that present the findings, conclusions, and recommendations of an audit engagement. A risk register is a tool that records and tracks the identified risks, their causes, their consequences, and their mitigation actions. References: CISA Review Manual (Digital Version), Chapter 2: Governance and Management of IT, Section 2.1: IT Governance