Question ID:PT81 S2 Q18 Passage:The consensus among astronomers, based upon observations of the surfaces of pulsars, is that pulsars are spinning balls of neutrons compressed into a sphere some 10 kilometers in diameter with a mass roughly equal to that of our sun. However, their observed properties are also consistent with some pulsars actually being filled with quarks, the building blocks of neutrons. Because the core of a quark-filled pulsar, unlike a neutron-filled one, would have an overall positive charge, it would attract a layer of negatively charged particles that could support a crust of neutrons. Stem:The statement that the core of a quark-filled pulsar would have an overall positive charge plays which one of the following roles in the argument above? Correct Answer Choice:AChoice A:It helps explain how pulsars could have neutrons on their surface even if they were not entirely made up of neutrons. Choice B:It forms part of a challenge to the claim that some pulsars may be made up of quarks. Choice C:It helps explain why some pulsars would not be readily recognized as such by astronomers. Choice D:It presents a new finding that challenges the consensus view of the structure of pulsars.  Choice E:It points out a problem with the view that pulsars have a mass roughly equal to that of our sun.