Instructions:
Question:
Book answer:
My answer:
歴史の本やドイツ語の辞書Xは机の上にあります。
I don't think など is compulsory, yet the book answer makes it seem as it were the case. To reach this conclusion, I just looked up a similar sentence from another book:
私は歌舞伎や能は観ません。
If は wasn't there, then など is required, right?
歴史の本やドイツ語の辞書など机の上にあります
The English version explicitly says "etc.", which is a rather strong word that indicates there are other things on the desk. You should reflect that using など. When there is "among others", "etc." and such, you basically need など.
You may believe や on its own functions as "etc.", but や does not explicitly state such a nuance.
Difference between と and や～など
Allows the listener to infer that, while you only mention Japanese culture and history, you are not implying that is the only thing you may be liking.
"You are not implying that is the only thing" is different from "You are explicitly saying there are other things", right?
If we leave aside the question of how much meaning we should read out of “etc.” in the English sentence and purely look at the Japanese sentence, など is indeed optional. Your sentence is perfectly fine.
歴史の本やドイツ語の辞書は机の上にあります。
The version with など sounds more formal.
Your last sentence sounds incomplete. You still need は.
歴史の本やドイツ語の辞書など机の上にあります。(?)
歴史の本やドイツ語の辞書などは机の上にあります。
In your other example, は can be replaced with など.
私は歌舞伎や能など観ません。
However, this など, used in a negative sentence (or in a rhetorical question with a negative implication), doesn’t only list examples but implies that the speaker thinks the things listed are unimportant. なんか is a more colloquial version of it.
を is necessary in an affirmative sentence. This など is neutral.
私は歌舞伎や能などを観ます。
