Translation:There is a dog.
If you typed in "It is a dog", you're incorrect (because "it is a dog" would be 犬です in Japanese), and Duo was trying to suggest the closest thing it had in the list of accepted answers.
As for why "It has a dog" is correct, note that the sentence here literally means "a dog (=犬が) exists(=います)". You'll also notice that there is no topic particle は in this sentence, meaning the topic has been omitted and can therefore be implied.
If you include それ as the generic pronoun for "it", the sentence becomes 「それは犬がいます」 which is literally "as for that (=それは), a dog (=犬が) exists (=います)." If you think about what it means for a dog to exist for something, you could say "a dog exists (among its possessions)". In other words, "It has a dog".
That's a good question. Most of the time we just say "it depends on the context" in a hand-wavy way, and it often does, but in this case, I think there is a subtle yet significant shift in focus in the English sentence when going from "a" to "the".
In "There is a dog", the new information conveyed to the listener is "a dog". It exists, but we don't necessarily know anything specific about it; the fact that it exists is most relevant.
If we say "There is the dog", presumably the listener already has some knowledge that a dog exists, because we're referencing a specific one. The more relevant fact now becomes where the dog is, "there".
In Japanese, this change in meaning isn't so subtle, with "There is the dog" being translated to 犬は(あ)そこです。
います is a verb, but です is something called a "copula" that acts like our English verb "to be".
In general, です needs to attach to a noun or adjective directly and you would not put a particle directly in front of it.
犬です。 (inu desu)
(It's) a dog.
Regular Japanese verbs like います require particles to show the relationship between the words in a sentence.
犬がいます。(inu ga imasu)
A dog exists. / There is a dog.
The が marks the subject of the sentence. In this case it tells us that the thing that exists is a dog.
In this particular case, it sounds more appropriate to use が because you are stating new information to the listener, but if you were to use は in these cases, since が is expected, then a contrast appears. The difference goes like this:
「犬がいます」"a dog exists".
「犬はいます」"as for a dog, (it) exist" or "dogs exists (in contrast to other things that could be there)".
For this section of duo, you will find a pattern of は being used for questions and negative sentences, and the use of が for sentences that express new information or describe the state of something (existence, adjective, etc). Obviously, these are not hard rules and you will find exceptions, but it is a good way to get past that initial barrier so you can start seeing the difference of usage in は vs が across the language.
犬はありますか？ "are there dogs?" or "do you have dogs?". Question.
犬があります "there is a dog" or "I have a dog". New information.
犬はどこですか？ "where are the dogs?". Question.
犬は外です "The dogs are outside". This one might be confusing, but in this case は is passing the focus of the sentence to the important part of the sentence. 外です is what you want to say, while the topic 犬は is there just for context. は in this cases is expected, similar to how sometimes "the" is expected in English.
それは犬じゃないです "that's not a dog". Negative
犬が好きです "I like dogs". Description of a state.
For birds and other small animals, the counter is 匹. Depending on the number of animals you want to say, the pronunciation will change slightly. I think this is due to a phenomenon called "rendaku", which is very prevalent in Japanese. Anyways, pronunciations from 1 to 10 are:
So, Japanese is a very context-dependent language. This phrase really is used in contexts where it means "There is a dog", and in other contexts where it means "I have a dog", AND in other contexts where it means "Dogs exist", AND ... well, hopefully you get my point.
Consider it this way. If someone asked you, "Do you have any pets?" and you answered "Well, there's a dog in my house", in English, you'd be thought of as a smartarse, but the point would get across: you own a dog. In Japanese, the point gets across, and you sound like a normal person because that's kind of how Japanese people prefer to communicate (indirectly, I mean, not like smartarses).
It depends on what your "incorrect" answer was; Duo tries to show you the "closest" "correct" answer to that. I suspect that "He's a dog" is in the bank of correct answers for much the same reason "It's a dog" is, which I've discussed at length on other comments already; check them out!
In this sentence, が is behaving as the subject particle, which means that it indicates "the thing that does the verb".
Because particles are postpositions, unlike the prepositions we're used to in English, が points at 犬 and says "a dog does it" or "a dog will do it". The "it" here is the verb, います, so the sentence becomes "a dog (=犬が) does exist (=います)" or in normal English, "there is a dog."
Yes, that can work. Discussed above: https://forum.duolingo.com/comment/23014495?comment_id=25364650
"There's the dog" is pointing out the location of the dog. The location is "there".
"There is a dog" is not pointing out a location, it's talking about the existence of a dog. "A dog exists", though we don't know where it is, because "there" is not a location, it's the existential there.