Answer:
B. an isosceles triangle
Explanation:
As we know that
When a plane moves through the cone's axis of rotation, then the resulting cross-section is a triangle with one vertex as the cone's vertex and the triangle's two sides through the vertex A are identical.
Where the base of the triangle is equivalent to the circular base diameter of the cone, and the two congruent sides of the triangle are equivalent to the slant height of the cone
Hence, the correct option is B.