Translation of "Mark's" in French

His mark's lowering was progressive.

L'abaissement de ses notes fut progressif.

Mark's book is very interesting.

Le livre de Marc est très intéressant.

And Mark's leading the charge on fixing Facebook.

Et Mark mène le combat pour corriger Facebook.

And at the first bend in that river, Mark's surgeon told us

Le premier obstacle sur ce torrent est apparu sous la forme du chirurgien de Mark