I believe the answer is:
(1) The work must be " fixed in a tangible medium of expression ."
(This means the work must exist in some physical form such as writings, audio, drawing, photos, or videos, for at least some period of time.)
(2) The work must be original
(this mean that the one who propose the copyright must be the person who made the creative work or has been reauthorized by the original creator,)
(3) The work must be the result of at least some creative effort on the part of the author.
(which mean that more than one person could obtain the right to use the copyright as long as they both involved in the creation)
