Subordinate clause is the answer
The correct answer would be - A: unique
Two things to keep in mind when you're deciding whether to use formal or informal English are the B) occasion and the audience.
Of course you are going to change the way you talk depending on whether you are speaking to your friends or to your teacher - usually with the teacher you are going to use more formal English.
Occasion is also important - you won't speak in the same manner at a party and a cocktail.
There’s a lot I can’t even think of one to be honest but ummm “valid” I think the word will become a concrete part of the English language. Just cause it sounds right yuunoo
