Are we submitting renders of each object, or the .blend file?
It can be renders of each object or a render of a scene with all the objects in it. No need for .blend files, as far as I know at least.
Also the exercise page will only let you upload a single image if I'm not mistaken,so if you're planning on doing a render per object, be sure to make a collage of the images into one single image file so you can upload it.