Explanation
According to the System Demo article on the Scaled Agile Framework website, system demos provide objective evidence of built-in quality and compliance. The article states that "The System Demo is a significant event that provides an integrated view of new Features for the most recent Iteration delivered by all the teams in the Agile Release Train (ART). Each demo gives ART stakeholders an objective measure of progress during a Program Increment (PI). The system demo is part of the inspect and adapt cycle and provides ARTs with the opportunity to assess their current state, adjust, and improve. The system demo also provides feedback on functional and nonfunctional requirements, such as compliance, performance, security, and usability." Therefore, the correct answer is C, system demos. The other options are not accurate, as they are not the events that provide objective evidence of built-in quality and compliance. PI planning (A) is a face-to-face event that serves as the heartbeat of the ART, aligning all the teams on the ART to a shared mission and vision. Backlog refinement (B) is the process of breaking down, estimating, and prioritizing the backlog items. ART syncs (D) are meetings that facilitate cross-team collaboration and alignment.