It rejected "would you help us clean the bathroom". Neither "would" nor "could" nor "can" is literal. Literally, it means "do you help us clean the bathroom" or "are you helping us clean the bathroom". But it is being used in the sense of asking for help. In that case "would", "could" and "can" are equally acceptable, indirection being a polite way of expressing an imperative.
Very much agree with you with regard to these exercises where "can" is the only English version accepted. That simply is not the only valid translation.
To try to get around Duo's requirement, I tried an even simpler translation, at least, simpler in the sense of using the fewest words: "Help us clean the bathroom?" In this case the "would you/will you" part is implied. Yet that answer was ALSO rejected (I reported that it should be accepted), and it supplied the completely unnatural "You help us clean the bathroom?" as the correct answer (which I reported as unnatural).
I agree that there are several ways of making a polite request in English, and all of them are as acceptable as using "can" (some of them arguably more polite). I also think the literal translation of "are you helping us clean the bathroom" should be accepted, too (given the absence of more specific context).
Apparently the database has been expanded since two years ago, as now "would," "could," "will," and "can" are all viable options. There are 124 solutions sentences in the database as of this writing, with multiple options for "bathroom" also.
Here's the sentence that covers your construction:
- [Can / Could / Will / Would] you help us clean the [bath? / bathroom? / bathtub? / lav? / lavatory? / loo? / restroom? / toilet? / washroom? / W.C.? / WC?]
It's not in front of a verb, it's following it.
There are a number of verbs in Spanish that require the prepositional a after them when they're immediately followed by a noun or a verb in the infinitive.
So when you use ayudar followed by an infinitive, you need to insert an a after the conjugation of the verb - think of it as 'can you help us to..."
Here's a list of verbs with this condition:
"Will you help us clean the bathroom?" accepted as at 11-Sep-2018.
I think 'Would' is probably used more often these days. 'Can' often gets a retort that "I can (i.e. know how to or am physically able to) and that's the answer to your --- question".
I try to lessen the fear or distaste of getting it 'wrong' by DuoEnglish and sometimes deliberately type what I think is a good expression (as a contribution) then hope that DL will eventually assess its merit.
What would it have been if it actually was "can we help you"?
I think that would be "Podemos ayudarte" or maybe also "Te ayudamos".
It is critical to look at the conjugation of the main verb. That is how you identify the subject, more so than the order of the words. In the original Spanish sentence we have ayudas, which is conjugated for tú, so we know it should be "you help" and not "we help".
More correct English would be "help us to clean" because it's the infinitive being used. When we leave out the "to" in English it's just because we are using lazy language; quite acceptable, in my opinion, except that I am old and was brought up with a more formal brand of English. It is more natural for me to use the infinitive but DL's English is so poor that it makes me afraid to use correct English. I have been marked wrong, in the past, for using "better" English. For instance, "how many rooms has this house?" The accepted answer was, "how many rooms does this house have." Having been taught that sentences shouldn't end with a hanging verb, I was quite upset to lose a life because DL doesn't recognize good English. This doesn't really matter because I am learning Spanish, not English, but I can't help wondering what the actual English course is like for those learning it as an added language. If the English is low quality, then it makes me wonder about the quality level of the Spanish course. Well, I guess one shouldn't complain. After all, it is better than learning nothing at all.
It's not "more correct", but it is also correct. In this case, clean is a bare infinitive. We use them all the time in English. The best example is with modal verbs like can or must. They require bare infinitives. Using he must to sleep would be wrong.
There is no grammar rule about a "hanging verb".
How much food did you eat?
When did you sleep?
Where has he gone?
It's not possible to avoid ending most questions with a verb. That's how English works. The "how many rooms has this house?" is regional English and not standard.
The English used in the course is good English. Not everyone uses the English language the same way and sometimes that means a sentence will look slightly "off" to some. That doesn't make it wrong.