Please somebody tells me why isnt good: a mouse is eating bread? Til now present cont. form was okey.
How can you tell the difference between "je" (present) and "je" (present continuous) ??
Present Simple vs Present Continuous? "eats" vs "is eating". There's none.
OK, you can use the habitual verb "jadać" (Mysz jada chleb = The mouse eats bread) to make it very clear that it's Present Simple, but the 'normal' verb "jeść" and the sentence "Mysz je chleb" also works perfectly fine for "The mouse eats bread".
Most Polish verbs don't show a difference between Present Simple and Present Continuous. Only Verbs of Motion (+ the notion of 'wearing') do, and there are some habitual verbs, but they're not obligatory and they're not even taught here.
I don't understand these translations. Once "a mouse" i s correct, another time no! It must be "the mouse"... May I ask why? In polish sentence like "Mysz je chleb" there is no context suggesting that its a specific mouse or not, so I think both "a" and "the" should be correct, because we do not know anything but whats given.
Both "a mouse" and "the mouse" are correct, both should have worked.
Either it was a bug, or perhaps you had something wrong somewhere else and Duo corrected it to the only starred answer here which has "The mouse" at the beginning. But "A mouse" is also correct.