Translation:I forgot to take my dog out, so it is angry.
Thinking about it more, for a dog that lives mostly inside, especially where winters are cold, the other reason to "take your dog out" is for it to go to the toilet.
But in that case you don't "take it out" you would use either or both "let" and "outside". (For a cat you can "put it out" but I don't think we use that for dogs.)
Don't need to use "outside". "Who let the dogs out?" (https://en.wikipedia.org/wiki/Who_Let_the_Dogs_Out%3F)
Many problems here. 1. A dog should be referred to as him or her here. 2. "牠" should be used instead of "它". 3. "了" is misplaced. The better sentence is "我忘记带我的狗出去了，所以牠很生气。" (4.) Although "take my dog out" doesn't sound natural, it's the most accurate translation. If you're a French speaker and would like to learn Chinese in your mother tongue, comment on Duolingo or my profile. This will encourage them to launch the course!
"他" has the human radical and is used for persons of indeterminate gender as well as for males. It would be used for all people, but Chinese writers in the early twentieth century wanted to emulate Western literature's access to "she"/"her". One particular linguist and poet, Liu Bannong, is credited with coining "她", or perhaps we could say with cursing the Chinese language.
But now what's emerging as a "genderless" third-person pronoun in writing is the word "ta", written in Latin script just like that.
Well, yes. It's just that that's what the word order implies ... and even if were the case that you were taking someone out on a date, you'd put 'out' after the subject: "I'm taking my GF/BF/dog out." Keeping 'out' right after the verb - "I'm taking out my GF/BF/dog" - sounds strange grammatically, at least in American English. Now, dating one's dog sounds strange in another way altogether! :-)
I don't think it's wrong, though I agree that it does sound a little awkward here, for some reason, though not that it really points toward dating (as you seem to concede in part).
There are certain phrases where the construction is a bit more at home – "take out the trash", "take out a mortgage", "take out an insurance policy", etc.
It could be a matter of emphasis, i.e. that the "out" is more emphatic when "taking someone/something out", and the "someone/something" is more emphatic when we say it the other way.
It could also be a matter of durative result. When I take my dog or my girlfriend out, we spend time out. When I take out a mortgage, it doesn't matter that the mortgage is "out", it matters that I have a mortgage. "Take out the trash" doesn't necessarily fit this pattern, though we could say that it doesn't matter that the trash is "out", per se, but that we've dealt with the trash.
That said, if the object of "take out" is long, putting it after "out" might be better in any case: "I forgot to take out the dog that bit me after Christmas dinner last year when I tried to feed it some turkey." It's a strained example, perhaps, but it'll do to make the point.
Edit in response to your response below: I'd allow it as grammatically correct, as it doesn't strike me as awkward enough to disallow. Not even close.
It's certainly understood; that's not the issue. The point is whether the original sentence "I forgot to take out my dog" sounds awkward or not. In American English, it does. Perhaps British English is different.
If a sentence sounds awkward, then it should not be accepted by Duo as a possible translation - unless there is absolutely NO BETTER WAY to say it and still get the point across in English. That's the crux of the question here. We could talk all day about possible wording, how it sounds best, or what words other words that sentence construction does sound good with. But I have no desire to do that. :)
"Take" is more usual for some reason.
"Bring" sounds as if perhaps you were going to bring it someplace with you, and you've just now realized that you're out without your dog, in which case, it's unclear how you can tell that it's angry.
And what's more, "bring out my dog" sounds like you were intending to put it on display, as opposed to "bring my dog out", which sounds more as though you were going to spend time out together — at least to my ear.
Whether you use "了", and where you put it in the sentence, can depend on the verbal aspect or other nuance you're trying to communicate.
Here are some grammar articles about "了":
Duolingo,I know this is correct English, however, this is the 21st century, and you still refer to an animal as a "it"? Like they are things, with no sexual attributes? Duolingo, wake up, and promote progress. Even in China things are changing and less and less eat dogs. Again I know this is a correct grammatical form, but languages are created my Humans, they grow, grammar comes after creation. That's a political choice. If you claim you are progressist, then assume.
But how else should we translate the sentence in English without making an assumption, since there's no indication of the gender in Chinese? Unless you're suggesting Duo should ne actively trying to make the Chinese more 'progressive' instead of teaching us how it's actually spoken?
Also, I do find it interesting when people judge 'progress' on the basis of the size of a small minority of people who sometimes eat one particular species, while saying nothing about the treatment of all the other species kept and slaughtered.