Answer:
plane parallel to the circular base, not passing through the tip of the cone: circle
plane parallel to the circular base, passing through the tip of the cone: A point
plane not parallel to the base, not passing through the base, and making an angle with the horizontal that is less than that made by the slant height of the cone: an oval that becomes more elongated as the angle with the horizontal increases
plane making an angle with the horizontal that is greater than that made by the slant height, passing through the tip of the cone : an isosceles triangle