How do we know that 'Some old planetary bodies..' - Solid Surfaces?

@iameunkyoung@gmail.com, Let's look at (E) and (C). (C) says, "Some planetary bodies whose cores generate enough heat to cause volcanic action do not have solid icy surfaces." It's true that we know that some planetary bodies with volcanic activity have solid ice surfaces. However, based on this, we still cannot conclude that there are some other planetary bodies with volcanic activity that do not have icy surfaces. We don't have enough information, so this is why (C) is out. (E) says, "Some very cold planetary bodies have cores that generate enough heat to cause volcanic action." We know that Europa is extremely cold, and because it doesn't have very many craters, we know that it has volcanic activity. Thus, (E) must be true. Recall that 'some' is at least one. If we know that Europa has volcanic activity, then it's true that 'some' very cold planetary bodies must have cores that generate enough heat to cause volcanic action because Europa is a member of this group. Hope this helps. Let us know if you have any other questions!

In the lesson, there was an example where it was said that when you have a some statement like PB some SS then it is also possible that some do not have SS. I made a note of this from the example, that when you have a some statement saying something is true that you can also infer that it is not true...since it's a some statement. Some do is equal to saying some don't. Can you please explain this further as this directly contradicts what was said in the lesson.