Answer:
D
Explanation:
I have no idea how to explain this, but I'll try my best. Let me know if you want further clarification.
When you're slicing parallel to the base, it would mean "in line" with the base if that makes sense. If we were to draw a line on where we would slice it, and another repersenting the base, neither line would ever touch.
So looking through each possible answer, if we were to slice each shape parallel to the base, only D would produce a circle.
Again, sorry about this sloppy explaination.