New answers tagged declension
The usual expression is im selben Jahr, i.e. the article contained in derselbe is absorbed by the preposition in the normal way. The same is true for other relevant prepositions (am selben Ort, zur selben Zeit) and for the accusative (ins selbe Zimmer). It is possible to keep preposition and article separated for emphasis or rhythm (in demselben Jahr); this ...
I think the Wikipedia page is wrong about point III. According to the German version of the same article Anmerkung: Hier gibt es keine Neutra which is literally saying that in group III there are no neuter nouns.
Take all relevent classes, then note down one word of each class in all cases, both singular and plural. Then learn it by heart. Here's a link to a table that I have created for learners of German, I hope it helps.
As a native speaker I can assure you your sentence is grammatically correct. The case is singular (one book), neutrum (das Buch) and accusative (object only acting passively). Read this Flexikon for all kinds of declensions.
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