Question ID:PT21 S2 Q13 Passage:Astronomers have long thought that the irregularity in the orbit of the planet Neptune was adequately explained by the gravitational pull exerted on Neptune by the planet Pluto. The most recent observations of Pluto, however, indicate that this planet is much too small to exert the amount of gravitational pull on Neptune that astronomers once thought it did. Stem:If the statements above are true, they provide the most support for which one of the following? Correct Answer Choice:DChoice A:Neptune is somewhat larger than scientists once believed it to be. Choice B:The orbit on Neptune is considerably more irregular than scientists once thought it was. Choice C:There exists another, as yet undiscovered planet with an orbit beyond that of Pluto. Choice D:The gravitational pull of Pluto is not the sole cause of Neptune’s irregular orbit. Choice E:Further observations of Pluto will eventually show it to be even smaller than it is now thought to be.