The picture below illustrates a special type of conic section called a circle. Which of the following offers the best description of how a circle is formed?

A. The plane passes through only one nappe of a right circular cone
and is perpendicular to its base.
B. The plane passes through the vertex of a right circular cone.
C. The plane passes through only one nappe of a right circular cone
and is parallel to its base.
D. The plane passes through both nappes of a right circular cone and
is perpendicular to its base.