The hint for "leabhair" in this sentence includes "books." Why, then, can this sentence not be translated as "She is using the books?"
An object of a verbal noun that follows the verbal noun is put into the genitive; the genitive singular of leabhar is leabhair. Since the nominative plural of leabhar is also leabhair, the dictionary hints for leabhair includes both “book (genitive singular)” and “books”.
Just in case any one's wondering, the genitive of 'books' is 'na leabhar', so it would be "Tá sí ag úsáid na leabhar" ~ she is using the books
What about " she is using a book", is it " tá sé ag úsáid leabhair?" or "leabhar"
The genitive of leabhar is leabhair so "She is using a book" is tá sí ag úsáid leabhair.
A different problem with this item ... For the "Type what you hear" version of the challenge, it seems (to my ear) that what is being presented by mistake is the audio from a different, but similar item: Tá sí ag oscailt a leabhar.. I got caught three or four times on this until I figured our the problem. After I finally got the desired sentence in and accepted so that I could go on with the lessons I reported that "The audio does not sound correct." For whatever good that might do.
The audio on this exercise is very clearly correct - I just played it for two other people who don't use Duolingo, and therefore aren't even "tuned in" to this speaker, and they immediately identified the audio as Tá siad ag úsáid an leabhair.
Thanks for checking this out. I am happy to accept the opinion of the experts that I am raising a false alarm here. There certainly is a lot to learn in this particular lesson — can't say I'm not getting my money's worth. :-)}