The correct answer is: B. how well the material concentrates electrostatic lines of force.
A dielectric is an insulating material that can be polarized by an electric field. The dielectric constant of a material is a measure of how well the material concentrates electrostatic lines
of force. A material with a high dielectric constant will concentrate electrostatic lines of force more strongly than a material with a low dielectric constant.Option A is incorrect because the dielectric constant is not a measure of the amount of voltage a material can withstand before breaking down. The amount of voltage a material can withstand before breaking down is called the breakdown voltage.
Option C is incorrect because the dielectric constant is not a measure of the amount of opposition to the current flow. The amount of opposition to the current flow is called the resistivity.
Option D is incorrect because the dielectric constant is not a measure of how well the material concentrates magnetic lines of force. The amount of opposition to the magnetic field is called the permeability.