Clarification about particle は


I had to translate these 2 questions:

> "Is this Chinese (language)?"  
>  "Is this sake?"

And I translated in this way:

> それは中国語ですか。  
>  それは酒ですか。

But the book solutions were

> それ中国語ですか。  
>  それ酒ですか。

Is this a mistake or it is possible not to use the particle in the polite
form? I wonder if it is correct or it's a grammar mistake.




It's the type of “grammatical mistake” that's extremely common in speech. In
absolutely proper grammar the “は” should be there, but think of it like “This
Chinese?”, people say that all the time but it would be “Is this Chinese?”
with more proper grammar.

Also, the Japanese word for “sake” is “[日本酒]{にほんしゅ}”; “[酒]{さけ}” means any
alcoholic drink in general and this specific pattern, more commonly used as
“お酒” typically means “Is this alcoholic?” in my experience.

