For a long I wanted to know how to say the term register in chinese, namely linguistic register. And then all of a sudden, many years later, when a teacher was lecturing me about some words usage she all of a sudden dropped a 语体 which was something I had never heard. I had looked up register before and only found 语域, which is something that is not used, or at least rarely used in the academic community but not among the teachers who I spoke to. (The difference between language teachers and language professors is alarming. Alarming that both are so bad.) Anyway, I looked up 语体 and its not really "register" its more like style, but since it's the thing your teacher can understand and in theory other people may accept, I reccomend its use.
Note. Not an hsk question, just useful.