Question

why must parachute have a hol e

Answer 1

that the air must enter and come out of it in order to make it fly in the sky.

Answer 2

All because of the drag of the parachute. So if that drag is so important, if pushing down as much air as possible is the key to slowing a fall, it doesn't make sense that round parachutes have holes in them. The holes let air slip through and continue on its way without slowing the jumper down.

hope it helps!!