Is “a bird” an subject, verb or object

I believe a "a bird" is a subject because I did process of elimination. It can't be a verb, because you cannot "do a bird." It depends what the context of the sentence is as well. Is there a clear object, or subject? Otherwise, I would say subject.

i believe it is d.) previous creature

hello there! there might be some substitutes that dont have experience with students. they only register for having a job. depends maybe on the old people or younger people

hope this