Translation:Nobody is reading the difficult book.
leest is to read, reads..Why is the correct translation: is reading, instead of reads...In my translation: Niemand leest het moeilijk boek, I interpreted as Nobody reads the difficult book. Suggestion because the book is difficult, no one one reads it. Nobody is reading the difficult book, suggests a difficult book is is not being read, which could or could not be due to the book's difficulty.
Because the English present progressive "is VERBing" is not well represented in other languages. Both "is VERBing" and "VERBs" translate to Dutch/French/Spanish third person singular present. In English we can use the nuances to show that something is currently happening (present progressive) or that something happens habitually (present). The same concept is shown in other languages in other ways, not through verb declensions in present tense.
@AbigailNat: But it is not currently happening at all! It is a fact, an observation (of something that perhaps already lasts three years or so.....). The observation of ..... something that actually has never happened all those years....!
Now you may say, "Yes, but exactly the fact that it "last" (= in Dutch "duurt") for a long time, indicates that it is an ongoing process: that justifies the use of the "verb + ing-form", but I find that far-fetched.
I have the impression that English speakers use the present progressive much more often than really necessary: automatically, without thinking.
In addition, Duolingo often acts inconsistently in this course (which makes it even more confusing than it already is).