@esther, if you read the fine print on the assignment, you’ll notice that (as usual) there is a limit of 10 pictures per photographer.
• How to Submit: Members can follow the A, B, C process outlined here. (Instructions for non-members can be viewed here.) You can submit up to 10 photos.
(emphasis mine)
Yes, narrowing it down to 10 favorites can be real hard! I know the feeling!