Blonde parachute training

[rebbonk]

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 recognise the faces of people on the ground."

After pondering his answer, she asked,

Spoiler:

"What happens if there's no one there I know?"