i wrote "their synagogues are big and nice" and it was marked as wrong because i didn't write "Their synagogues are big and pretty". i speak fluent hebrew and fluent english and both "nice" and "pretty" mean "יפה " in hebrew.
If it's helpful to anyone - in Minnesota and I think generally around the USA - we would more likely refer to a building as beautiful, probably not pretty.
This program is inconsistent with acceptable translations for בית כנסת, I usually say "temple" or "shul" in English, and I've noticed these words are sometimes okay and sometimes not.