1. If the friends had not gone in the USA, they would have not visited Death Valley.
2. If they had come to Death Valley in winter, they would have been able to see more.
3. If they had gone there, they could have died of heatstroke.
4. If Martin had taken more than a liter of water, it would have helped.
5. If the rangers had come ten minutes later, they would not have been able to save him.