Translation:Did the guard assist you? No. She didn't assist us.
Because Klingon differentiates singular from plural and you are in a learning situation, we do not allow the use of the singular "they" in this course, so the software can tell whether you mean singular or plural. If you use the singular "guard" in your English translation, you must use either "he" or "she" in the response.
However, since plural markers are not required in Klingon it IS possible to translate the Klingon sentence with plural subjects. "Did the guards assist you? No. They didn't asssist us," is also an accepted answer. But you must put the -s on "guards" to match the "they" in the response.
Outside Duolingo, if you translate ghaH as they, in context, there's nothing wrong with that, and if you don't know a person's English pronoun, they is probably the best choice, but for the purpose of teaching all the prefixes on this course we're pretending they can only be 3rd person plural.
Whenever a translation is ambiguous, e.g. ghaH can be he or she and you see can be bIlegh or Sulegh, just pick one of the possibilities. If it's not accepted, and you've double-checked your answer for typos, report it with the "My answer should have been accepted" option.
It is very difficult to teach just through example sentences. There is a lot of overlap between the words boQ and QaH, but the implication in QaH is that you were unable to do it yourself and their "help" was required and the implication in boQ is that they merely assisted you to accomplish what you were capable of yourself. To try and impress that difference through the Duolingo method, we have been careful about whether "assist" or "help" is shown in the Best Translation. I think we have added all the variations for all the Alternate Translations throughout the course, though. If you happen across one that seems to be missing, feel free to use the flag report.
lI- is the prefix for third person subject (regardless of number) and second person plural object (he/she/it/they - y'all). So the initial question (lIboQ'a' 'avwI'?) could be asking either "Did the/a guard assist y'all?" or "Did (the) guards assist y'all?" One of the nice things about a sentence like that in Klingon is that you don't even have to know how many guards there were to ask the question. However, in English you have to pick a number of guards to ask about and you are forced to pick either the singular or the plural. Perhaps there is a trick you can use in English to ask a similar type of question that is open to either singular or plural guards with something like, "Did any guards assist y'all?" Come to think of it, we should probably allow that translation of the initial question.
nu- is the prefix for third person subject (regardless of number) and first person plural object (he/she/it/they - us). The people that the initial question addressed as "y'all" are now responding as "we/us". So the response nuboQbe' still has the same guard or guards doing the action, but now the responders say "he/she/it/they didn't assist us." In Klingon both the question and response leave the number of guards completely ambiguous, but again, in English we have to choose whether we are going with singular or plural. I suppose in a real conversation you could say, "They didn't assist us," which leaves it ambiguous as to whether you meant plural "they" or the singular non-gender-specific "they". However, while we encourage use of singular "they" in real English conversations, we discourage its use in this course so we can be sure that students are keeping clear on the singular and plural prefixes where they differ.
In a real conversation, if the number was important and not already clear, you could first say you know there is only one guard or multiple guards or whatever. Or specify wa' or -pu' in the question. Or maybe previous discussion has already made it clear. Or maybe you don't care about the number, so you are intentionally leaving it vague. But Duolingo lacks that kind of context, so it is impossible for us to force you to guess if we meant singular or plural guards. And thus, for this exercise, variations that assume just one guard are accepted and variations that assume multiple guards are accepted. Which ever choice you make, you should be marked correct as long as you got the rest of the grammar correct. The only variations we don't accept are where you use a different number of guards in the question at the beginning from the number in the response at the end.