What encompasses Canadian Domestic Airspace (CDA)?

The correct response includes all airspace over Canada and its islands because Canadian Domestic Airspace (CDA) is defined as encompassing the entirety of airspace within Canada's geographic boundaries, which covers both the mainland and its surrounding islands. This classification is essential for air traffic management and aviation regulations, as it allows for coordinated control and planning for all flights occurring within this area.

The other options are more restrictive and do not accurately describe the extent of CDA. By suggesting that only certain regions, populated areas, or major cities are included, they overlook the comprehensive nature of CDA that is essential for ensuring safety and efficiency in air navigation across the entire country.