USA stands for United States of America. I am not so sure if that was what your were asking or not.
Hi, the answer would be D - direct object. It cannot be the subject, because the subject of the sentence is "the essay". It isn't object of a preposition, as there is no preposition there. It is not a possessive, and given that this adjectival clause is a part of "the mountain", which is a direct object, it must be a direct object as well.
