What must a PIC comply with at all times during flight?

The correct answer is that a PIC (Pilot-in-Command) must comply with light signals and ground markings as prescribed in the Canadian Aviation Regulations (CARs) at all times during flight. Compliance with these regulations is critical as they provide essential guidance for safe operations in controlled and uncontrolled airspace. Light signals, for example, are used by air traffic control to communicate with pilots, especially in situations where radio communication may not be possible. Understanding and adhering to these signals is fundamental to maintaining safety and order in aviation.

In addition, ground markings also assist in navigation and safety on the ground, such as taxiways, runways, and holding positions. By following these regulations, the PIC ensures that they are operating within the legal framework that governs aviation activities and contributing to the overall safety of their flight operations. This compliance is not just about following laws; it is also a significant component of professional pilot conduct and operational integrity.

The other options, while relevant to a pilot's responsibilities, do not encapsulate the overarching requirement of compliance with regulations and signals that directly impact the safe flight operation.