The correct option is B several books written by them
Option B is the correct answer. The complete subject is indeed several books written by them, since they are being talked about in the sentence, justified by the use of the verb are lying. Option A is a part of the subject, not the entire subject of the sentence. The rest of the sentence is what is being said about the subject,i.e., it is the predicate. The statements of options C and D are parts of the predicate and, thus, cannot be the subject.