If submerged vehicle occupants cannot open windows and must escape through the doors after the car has sunk, what physical condition must occur before the doors can be pushed open?

1. The vehicle must be completely upside down
2. Water must fill the cabin almost completely (equalizing water pressure inside and outside / 内外水压平衡), allowing occupants to push the door open and swim upward
3. All electronic computers must completely submerge in mud
4. The engine exhaust system must fill with air