Where are the primary Blind Spots (Puntos Ciegos) located around a heavy commercial tractor-trailer or bus?

1. Only directly above the roof of the cab
2. Four major zones: directly in front of the cab below driver sightlines, directly behind the trailer/bus, along the immediate left side below the window, and a massive blind zone along the entire right side extending backward across multiple lanes
3. There are no blind spots if convex mirrors are fitted
4. Only inside the engine compartment