Question

Which intersection forms an ellipse?

A plane intersects only one nappe of a double-napped cone. The plane is neither perpendicular to the axis nor parallel to the generating line.
A plane intersects only one nappe of a double-napped cone such that the plane is parallel to the generating line.
A plane intersects both nappes of a double-napped cone.
A plane intersects only one nappe of a double-napped cone such that the plane is perpendicular to its axis.

Answer 1

The first option a plan intersects only one nappe of a double napped cone. The plane is neither perpendicular to the axis nor parallel to the generating line.