The correct answer is D. Pluto
Step-by-step explanation
According to the characteristics presented for the celestial bodies, such as the impossibility of cleaning its orbit by its small size and a rock surface without rings, the one that best suits these characteristics is Pluto. This can be explained as in 2006 Pluto was claimed to be a dwarf planet, which means it shares similarities with other planets but due to its size it does clear objects from its orbit and therefore it is not a planet. Also, Pluto is composed of rocks and ice, but different from other bodies such as Saturn it does not have rings. So, the correct answer is D. Pluto.