Duolingo would not accept my unaccented "Ou" as part of the correct answer. I do not have access to the special characters at times. I find this a bit irritating.
On my android phone I hold down the letter and all the possible versions of the letter show up for me to choose from, Macs do that too. On my pc Windows has Character Map program with all characters from all languages that you can cut and paste from. You can also use the alt key with Ascii codes or Unicodes which you can find tables of on the internet and save to your favorites.
Should there not be a liason between où and sont making the pronunciation something like ou zon?