The c-discriminant and p-discriminant are concepts used in algebraic geometry to study algebraic curves. They are important tools for understanding the properties and behavior of curves.

C-Discriminant:
The c-discriminant, also known as the characteristic discriminant, is a polynomial that characterizes the singularities of a curve. It is defined as the determinant of the Hessian matrix of the curve's defining equation. The Hessian matrix is a matrix of second partial derivatives of the equation with respect to the variables.

Envelope:
An envelope is a curve that is tangent to each member of a family of curves at the points where the family of curves is tangent. In the context of the c-discriminant, the envelope is the set of points where the curve has singularities. The c-discriminant is a polynomial that determines the equation of the envelope.

P-Discriminant:
The p-discriminant, also known as the polar discriminant, is another polynomial that characterizes the singularities of a curve. It is defined as the determinant of the Jacobian matrix of the curve's defining equation. The Jacobian matrix is a matrix of first partial derivatives of the equation with respect to the variables.

Tac-Locus:
The tac-locus, short for Tactangent locus, is the locus of the points of tangency of the tangent lines to a curve. In the context of the p-discriminant, the tac-locus is the set of points where the curve has singularities. The p-discriminant is a polynomial that determines the equation of the tac-locus.

Explanation:
The c-discriminant and p-discriminant both contain the envelope, which is the set of points where the curve has singularities. The envelope can be thought of as the locus of points where the curve "touches" or "collides" with itself. It is an important concept in algebraic geometry as it provides information about the behavior and structure of the curve.

On the other hand, the c-discriminant determines the equation of the envelope by computing the determinant of the Hessian matrix. Similarly, the p-discriminant determines the equation of the tac-locus by computing the determinant of the Jacobian matrix.

Therefore, the correct answer is option A, as both the c-discriminant and p-discriminant contain the envelope, which is a key concept in algebraic geometry.