Roman is a "de" word, shouldn't it be "die" instead of "dat"?
In constructions like "it is ... " or "that is ... ", Dutch always uses the het-form, regardless of what comes after.
Take a look at the end of this page: http://www.dutchgrammar.com/en/?n=Pronouns.De03
Is "dat roman is de langste" correct? It didn't accept it for some reason
First of all it is de roman, which would make it die roman. Other than that it's a different sentence.