I'm taking an online class for Algebra II, and the first lesson concerns right circular cones and the curves resulting from intersecting planes; conic sections. Over half of the questions talk about the plane in relation to the "edge" of the cone. The first question is this:

If a right circular cone intersects a plane that runs parallel to the edge of the cone, the resulting curve will be a(n) ____.

A. ellipse

B. circle

C. parabola

D. hyperbola

I've combed through the section and checked its key terms. They are: circle, conic section, ellipse, hyperbola, nappe, parabola, right circular cone, vertex.

I know, or at least I think, an edge is the line where two faces meet. So I assumed it was where the base and the lateral surface (am I using that term correctly? I mean the part that wraps around the shape) met. That is, I thought being "parallel to the edge" would be the same as "parallel to the base", etc. And so because over half of the questions mention this "edge", I failed the quiz spectacularly. Luckily I can retake it. Once.

TLDR What is the edge of a cone!?