The one shown as the best answer on the Android app on 24 Dec 2015 is "Why aren't children at school.". Though possible, it sounds a lot less natural without the " the" before "children".
when are genetive and prepositional forms of whose used in a sentence, i cant seem to thnik of examples or sentences for them
It's funny! I do not type, I just pick the answer in the boxes. Then they tell me:" you have a typo..."
For the same reason other sentences with negation have "not" instead of "no". Possessive sentences only seem an exception because of how they are structured ("there is no.." is a closer match than "Someone has something").
No, "ain't" is not correct grammar. Some speakers of English use it, and it is heavily used in some regions of America - but it is never correct, is used perhaps dialectically, and will always get you a steely glare from your grammar teacher. Instead, use "isn't" or "aren't" depending on the number - "isn't" for singular, such as, "Why isn't he at school?" and "aren't" for plural, such as, "Why aren't the children at school?"
Yes, you will see it there - it's pretty common in spoken English. However, it is not standard English. Interestingly, it used to be standard English - but it no longer is.
I was taught "'Ain't' ain't a word, and you ain't supposed to say it. Say 'Ain't' five times and you ain't going to heaven."
Yes, I was taught the same. This word, which was once commonly and widely used even in literature, was de-standardized. It is a common enough occurrence when a language “solidifies” — regional dialectical variations which are considered acceptable are eliminated in favor of a standardized, widely-taught format.
в and на are used with the Prepositional case of a noun when expressing location. A few nouns have a separate form for that (the Prepositional is also used with о and при).
Is it possible to discern between children AT school and IN school? By using в vs на? Or is it done via context?
Duo accepts either "at" or "in", so context is the only way to figure out exactly what's being discussed - and of course there's no context here.
It might be harder if there were context, because then you'd have to figure out whether "in" or "at" is appropriate.