The diagram below shows some subatomic particles. An outer circle, labeled X, surrounds three smaller circles; one of these is labeled Quark. The three inner circles are connected by a line from each circle to a point at the center of the large circle; the three lines resemble the letter Y.

Which of these statements best identifies the particle that is labeled with an X?
It is either a nucleus or a proton.
It is either a proton or a neutron.
It is either a neutron or an electron.
It is either an electron or a nucleus.