Noob needs a little help RE: Photo Image Sizes

Long time consumer of Pond5 images, but new as an artist.
As a consumer, I see a single preview image, but when I select that image I have XL-Sm as choices I can buy.

So, as a submitting artist, do I submit images sized appropriately, all with the same title? Or, do I submit a single hi-res image and Pond5 "magically" creates the lower res images?

Just unclear on the concept.
Thanks in advance,
Bob

I don't submit photos to Pond5, but do with other agencies, you submit the highest resolution you have, they will take care of the conversions for the lower resolutions.

Thank you for taking the time! Much appreciated.
Just what I needed to know.