Why was "sa" used here? It is the only example of "sa".

Question

Il faut toujours avoir sa carte sur soi. One must always have one's map on them.You must always have your map on you.

Answer

Bonjour Judy !

The reason you used "sa" here is that "carte" is a feminine noun, and that the possessive adjectives always agree with the *owned* object in French :)
The other examples were simply masculine ones, hence "son", or plural "ses".

However, I've decided to add a note to remove any ambiguity :)
I hope that's helpful!
Merci et à bientôt !

Answer

Bonjour Aurelie!  I kept pondering this lesson and finally figured out that my problem was the first example on the page:  "Tout le monde a son opinion."    I knew the owned object was feminine but forgot that since "opinion" started with a vowel I needed to use the masculine "son"!
It might be clearer to have a  "sa" answer in the first set of examples.   But then I wouldn't have reviewed the adjustment we have to make at times with words starting with a vowel or silent h!
I really have enjoyed your lessons.  They are very clear to a 78 year old French learner.
Merci et a bientot!

Answer

Oh, I see you already fixed everything.  Good job!
Merci et a bientot!