Then you can slow down yourself - Spend time practicing more than learning new lessons. I'm doing the same thing for my Greek course, as I still haven't got used to the alphabet yet.
I think he is referring to practicing more listening. I do that by clicking "Follow Discussion" button so I can return to practice.
Got it. If there is a plural classifier/number then book classifier is alos needed?
Seriously, we need native English speakers to check these answers. This solution sounds so bad. Any of the following would have sounded like fluent English but not this one. "Why are they publishing the book?... Why did they publish the book?... Why do they publish books?... Why are they going to publish the book?... Why are they going to publish the book?" But it's hard to learn when I don't really understand the intended meaning of this translation.
Well, except for "Why do they publish books?", all the translations you listed would be all legit, because Vietnamese has no grammatical tense, and all time references are done with adverbs and contexts, both of which are not present here.
For a language heavily dependent on context like Vietnamese, Duolingo, a translation-based platform, inherently does a really bad job. It is, as you can see, impossible to know the intended meaning. They could list all possible translations out, but that's certainly exhaustive and time-consuming (and data-consuming, too).
I have this problem with many of the sentences in this course, but not with this one. To me this sounds perfectly natural in the simple present tense "Why do they publish the book", since publishing can be an ongoing thing with new prints and new editions, etc.