There are many phrases that are not clauses. In this case, the words are not correct as either. "The big class is upstairs." That could work as a sentence, but I am not sure what it means.
Student or Learner
I heard from one of my teachers that the below sentence is correct as a phrase but it's wrong as a clause.
The class big is upstairs.
How that can be possible?
Marmoolak, please note that a better title would have been The class big is upstairs.
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