You may find this webpage helpful, http://www.french-linguistics.co.uk/lexcats/determiner.html
There is a bug which sometimes displays the answer to this as "He's a book". This is incorrect - the correct translation is "He has a book". Unfortunately we have no control over this, so please send a bug report and move on. Note that I don't mean the report button in the lesson, which only sends the report to the course contributors who can't do anything about it, but a bug report to Duolingo staff, which can be found at the link above.
From months ago but it still happens, it's a very long standing issue which has been driving us all crazy for ages... In asking for reports I don't mean the report button in the lesson - that only goes to the contributors in the Incubator who can't do anything about it (much as we wish we could!) - but a bug report that goes to staff (see the link in my other comment). Thanks for reminding me to clarify that!