"Peut-être était-ce vraiment mon imagination."
Translation:Maybe it was really my imagination.
The inversion is used for things other than just questions. Duolingo doesn't really explicitly cover this fact, but here is a brief list of some times it is used: http://french.about.com/library/weekly/aa110601.htm
If you look under III.B. you'll see that after "peut-être" you either do an inversion of the S-V or follow it with "que".
That's a good link Patlaf. The reason why you can use the V-S form with "peut-être" or "sans doute" is that they express near-questions, if you see what I mean. There really is a doubt there, so it is a polite way to prudently propose an explanation.
By the way, "sans doute" does not mean "undoubtedly" but "probably, maybe, etc..."
Was wondering also, had to listen several times in turtle mode and only worked it out by guessing given the context - sounds like it's run together "etɛz", whereas Larousse articulates it separately "etɛ-sə", http://www.larousse.fr/dictionnaires/francais-anglais/%C3%AAtre/31483?q=%C3%A9tait-ce#841452
I've found that you can't necessarily depend on the audio here. I've come across a few exercises where the regular speed audio has been incomplete and others where you simply cannot hear all the words correctly at regular speed and you HAVE to listen in turtle mode to get it right. The audio seems to be machine-generated. When in doubt I always double-check pronunciations with other sites.
'Imagination' (and all French words ending in -tion) is feminine indeed. However, if a feminine word starts with a vowel, the masculine possessive determiner 'mon' is used before it instead of the feminine one 'ma', so as to make the pronunciation prettier. But the noun itself remains feminine without doubt. So you will read a sentence like this : "SON amiE est françaisE."
So what is wrong with "It is possible this was truly my imagination"?
Is that just because it doesn't start with C'est?
Also the translation seems unnatural (I mean it's grammatically correct, but not natural), I would probably rephrase it as "Maybe it really was my imagination".
I am a bit confused about "mon imagination" because according different online dictionaries the french word "imagination" should be female. Therefore I would say "ma imagination". Seems I never understand the rules.