If there is one exact sentence taken out of the book and not referenced in quotes and exact source, that triggers copyright laws. So model doesnt have to reproduce the entire book, it only required to reproduce one specific sentence (which may be a characteristic sentence to that author or to that book).
If there is one exact sentence taken out of the book and not referenced in quotes and exact source, that triggers copyright laws.
Yes, and that's stupid, and will need to be changed.
Sure, but that use would easily pass a fair use test, at least in the US.