My sister didn’t leave the car key. As a result, I couldn’t pick her up at the airport

If my sister left the car key, I would pick her up at the airport.

If my sister had left the car key, I would have picked her up at the airport..

If my sister have left the car key, I would have picked her up at the airport.

If my sister had left the car key, I could pick her up at the airport.