Normally it should be Pourquoi a-t-il mal à l'estomac (1). But I would like to know if 'son estomac' is also okay.
If it is gramatically correct to say Pourquoi a-t-il mal à son estomac (2), does it make a change in the meaning?
Note that I got sentence (1) from Duolingo.com as the correct translation of Why does his stomach hurt?, where sentence (2) is marked wrong. In this link, however, there are hints that sentence (2) might be correct too. So what would you say on this?