I have to concentrate in order to not confuse Godzina with Godina (Serbian) and год (Russian). Wasn't rok something else too in Czech or in another Slavic language?
Why are an hour, a month and a year? I chise a hour a month and an year. In result my answer is not right!
It is an English language thing- a/an depends on how it sounds, not how it's written. "h" is silent and "y" is a consonant (Polish "j")