"It is normal that you chose a pretty watch."
Translation:Il est normal que tu aies choisi une jolie montre.
There appears to be some debate about il est normal and c'est normal.
It appears to be a matter of written vs spoken French and, as Duolingo tends to teach the first, it may explain why C'est normal que ... was not accepted.
DUO accepted "C'est normal...." from me several months ago for this very question....but rejected "C'est normal..." today. Very frustrating.