OOOOPS - I wrote "može" and was told I had the correct answer... There IS a big difficulty differentiating between ž and ř, but I believe it's because of acoustics - and because in some contexts, the two sound very similar - hardly any of the "R" sound comes through sometimes. Colloquial, or just an untrained ear?
Thank you - I thought it must be a matter of my ear. I can usually hear the difference very clearly, but sometimes I miss it, and "sea" was a new word! I was just surprised that I was told I was correct, but NOT that I had a typo - that I would have accepted without question. I really appreciate your feedback!