Take a look at it. We know it's a cone, right? So that answers your 3rd question. The base (or the part that it sits on if you put it down), is a circle. The other parts it can't sit on without rolling, so it has to be that circular side. And if that's a circle, that means that any line from the center to the outside 'circumference' is the radius. This means that the answer is A.
