What is the loop hole in the 13 amendment?

The 13th Amendment outlawed slavery across the nation, with a key loophole:

“Except as punishment for a crime whereof the party shall have been duly convicted.”

This paved the way for the country's burgeoning prison labor system and the world's largest prison population.

(i hope this helped umm. Brainliest please?)

can you give us the options

i would pick a. i think this is more of a personal question though.