what's the difference between "ena" and "mia"? they both translate to "a"
ένας is used for masculine nouns, μία for feminine ones and ένα for neuter ones.
The same difference as "un" "una" in spanish
Why is not allowed the continous form in the translation? Why can not it be "we are reading.."?
It is supposed to be allowed... It's one of the possible accepted translations. Maybe there was some other typo that got marked as incorrect?
Why in this case is there an accent on μία, but not always in other sentences?
It's practically the same. "Μία" mostly means "one", "μια" mostly means "a(n)", but it's not a big deal.