Parachute Training

On the first day of training for parachute jumping, a blonde listened intently to the instructor. He told them to start preparing for landing when they are at 300 feet.

The blonde asked, “How am I supposed to know when I'm at 300 feet?” 

“That's a good question. When you get to 300 feet, you can recognize the faces of people on the ground.” 

After pondering his answer, she asked, “What happens if there's no one there I know?”