Translation:Are klongats dangerous? Yes. Klongats are very dangerous.
It's wrong in Standard American English. There are dialects of English in which Klongats be dangerous would be perfectly grammatical, Black English for one. But this course only accepts Standard American English, with occasional allowances for British English, and in SAE, you must conjugate be in places like this.
Qob'a' tlhonghaDmey has tlhonghaDmey as the subject, so tlhonghaDmey are doing something. The thing they are doing is represented by the verb, Qob be dangerous. The -'a' means you're asking a yes/no question regarding their being dangerous. In Standard American English, you'd ask this as Are klongats dangerous? and that's the response the course is expecting. In Standard American English, you typically must put the be verb at the beginning for yes/no questions, and you must conjugate the verb. The correct conjugation of be for a third-person plural subject is are. Then you state the subject, then the adjective.
Ebonics, or Black English, has quite specific rules regarding its deviations from Standard American English. To those who do not speak it, it may seem like English spoken "wrong," and those who do speak it are probably unlikely to be able to explain exactly what the rules are (any more than the average speaker of Standard American English can explain their own grammar rules). But it's a hot topic among linguists, and there are many books explaining the rules.
If youre going to get into technical English, that's 'beith' which isnt an official word and it would be "art klongats..." which isnt used anymore. #Ænglish
Actually, that isn't quite correct either. 'Art' is the archaic 2nd person singular form of the verb 'to be,' and as such only goes with the pronoun thou. The subjects in this sentence are all 3rd person plural, therefore, "are" was/is still the correct form to use. If you're curious about the correct archaic conjugations, there's a table on this page:
I'll agree with you that "beith/be-eth" isn't a word. :-)