I suggest you to read the "Tips and notes" at the beginning of these lessons if you can. Somehow from mobile they doesnt seems available, check with the computer.
I think that plural is used only if we are not sure about the number. If we can understand the sentence correctly with the singular word then we don't need the plural form.
I listen to the audio 6-8 times and I heard szent. I listened again after I saw the correct answer and still heard szent. I know that szent would not make sense, but I could not figure it out from the audio.. Please review
Still doesn't accept "overhead" (more natural in English). I just complained.
Above? Above what? Few airplanes fly overhead - was my answer and rejected. One could say in good English: Few planes fly up above. Your correct answer sounds incomplete to me.