Planetary bodies differ from one another in their composition, but most of those in the Solar System have solid surfaces. Unless the core of such a planetary body generates enough heat to cause volcanic action, the surface of the body will not be renewed for millions of years. Any planetary body with a solid surface whose surface is not renewed for millions of years becomes heavily pockmarked by meteorite craters, just like the Earth' s Moon. Some old planetary bodies in the Solar System, such as Europa, a very cold moon belonging to Jupiter, have solid icy surfaces with very few meteorite craters. If the claims above are true, which one of the following must, on the basis of them, be true? ['Some very cold planetary bodies have cores that generate enough heat to cause volcanic action.', "Some of Jupiter's moons are heavily pockmarked by meteorite craters.", 'Some planetary bodies whose cores generate enough heat to cause volcanic action do not have solid icy surfaces.', 'If a planetary body does not have a heavily pockmarked surface, its core does not generate enough heat to cause volcanic action.']