They listen to what you say. The word pronounced as "сока" is "сока" and the word pronounced as "сука" is "сука". Context also matters because сука is Nominative singular and сока is Genitive singular: the structure of the sentence should be rather weird to make sense with either.
Every lesson have some tips and notes, but they are only visible in the web app. https://www.duolingo.com/skill/ru/Genitive-Case---1
Tips and notes
In Russian “I have” is expressed by «У меня (есть)» structure. The owner is in the Genitive case.
"The of-case". It is one of the most universal cases. How do you make the forms? Here is the regular pattern:
A zero ending means that the word ends in a consonant or a soft sign (which is just a way to show the final consonant is "soft"). In the Nominative singular, a Russian word can only have the following endings: а, я, о, е, ё ornothing ("zero ending").
GENITIVE OF NEGATION
If you use «нет» to say that there is "no" something or you do not have it, the object is always in Genitive:
У меня́ есть я́блоко → У меня́ нет я́блока
Здесь есть рюкза́к → Здесь нет рюкзака́.
"of" (possession): яблоко мамы = mom's apple"of" (amount): чашка чая, много чая = a cup of tea, a lot of tea
A huge number of prepositions requires this case. Yes, «у меня есть», «У неё есть» only use «меня» and «неё» because «у» wants Genitive.
For он, она and оно Genitive doubles as a non-changing possessive "his", "her", "their": его, её, их.
initial «н» is used for him/her/them with the majority of prepositions (doesn't affect possessives)
A little side note: some nouns of foreign origin are indeclinable. It means that all their forms are the same. Foreign nouns that end in о/е become like that (кофе, метро, радио, резюме), as well as all nouns that do not fit into Russian declension patterns (see above).
This includes female names that end in anything other than А or Я. A few -ь-ending names are an exception (Любовь and Biblical names like Юдифь).
So, all of the following names are automatically indeclinable: Маргарет, Мэри, Элли, Дженни, Рэйчел, Натали, Энн, Ким, Тесс, Жасмин.
I AM AWAY
Russian also uses the Genitive to state that someone is "away", "not there": Мамы сейчас нет. In English such use would correspond to "There is no mom at the moment", or even "There is no me now". We are not hard on that particular construction in the course, but it is important to know it all the same.
Added bonus: when a verb directly acts on a noun, the noun is called a direct object and is in Accusative. In Russian, only -а/-я feminine nouns have a unique form for it. Others just reuse Genitive or don't change the word at all (Nominative)
Russian uses.... let's call it "consistent" negation. It means that in negative sentences you are required to use "nothing" instead of "anything", "nowhere" instead of "somewhere" and so on. Let's meet the first of these pronouns:
У меня ничего нет. = I don't have anything. Она ничего не ест. = She doesn't eat anything.
You'll also notice that, unlike standard English, Russian has no rule against using double negatives.
Because it is a genitive case. Я пью сок (I drink juice ) - Is nominative У них нет сока (They don't have juice) - is genitive Я даю соку (I give to the juice) - dative Я виню сок (I accuse the juice) - accusative Я рисую соком (I draw with a juice) - Instrumental Я говорю о соке (I talk about juice) - Preposition case.
In case if anyone else is reading the notes here, a small correction seems necessary: Я пью сок (I drink juice), сок isn't nominative. Я пью + accusative. However, people can be confused because inanimate objects, masculine and neuter, do not change their form in accusative. Я пью водку. - I drink vodka. For instance, take водка in nominative, feminine noun, changes here to водку in accusative. The following link might be helpful when it comes to accusative case and its use: http://learnrussian.rt.com/grammar-tables/accusative-case-direct-objects/
Okay, I see many have noticed it's pronouncing it as 'сука'. (of course it helps to know what that is, you'll be even more delighted when the random Russian guy starts yelling that at you from the balcony. Maybe add a new skill for that stuff?)
But how should it be pronounced? 'сака'? 'сока'?
Since you are the first one to say that Duo doesn't accept one of those alternatives, I suspect that you had some other error in your answer.
The Duo computer tells you about errors in your answer not mistakes that you made. By that, I mean that it has no idea what you were trying to write. It just spots an error and reports it. It is indifferent to any claim that there was nothing wrong with that particular word, it was I wrote afterward that made it look wrong.
Eg: ......The don't have something..... The error in this sentence is not The. There is absolutely nothing wrong with The. Therefore the mistake is don't
The and don't can't go together. So it flags don't as an error. It can't possibly to expected to know that you left out the Y in they so it ended up appearing as The.
You may be thinking that you didn't make any mistakes in your sentence but as I noted previously..... you are the first person to say Duo does not accept one of the alternatives between don't and do not in this example.
Had you posted your actual answer it might be more clear where the error in your answer actually was. But just posting.... Duo is wrong.... , without copy/pasting and posting what you submitted and think was correct, has little value for us, for Duo and for you.
In Russian, "having" is most commonly expressed as an existence statement. If they have juice, you say the juice IS "at them".
The structure is У + who + есть + what. The preposition у requires the Genitive form of the noun or pronoun:
- мама → у мамы
- мальчик → у мальчика
- лошадь → у лошади
- я → у меня
- ты → у тебя
- мы, вы → у нас, у вас
- он, она, они → у него, у неё, у них (the initial Н is added after prepositions)
(though, we do not use есть when existence per se is not the main point: for example, when describing body parts, stating medical conditions or the amount of something)