The correct answer is B. Magnetization.
Magnetization is the process of inducing a magnetic field in a material. This can be done by applying a magnetic field to the material, or by heating the material to a high temperature. Iron filings are attracted to magnets, so they can be separated from a heterogeneous mixture by placing a magnet near the mixture. The iron filings will be attracted to the magnet and will be pulled away from the other materials in the mixture.
Sublimation is the process of a substance changing directly from a solid to a gas without passing through the liquid state. This can only happen if the substance has a very low vapor pressure. Iron filings do not have a low vapor pressure, so they cannot be separated from a heterogeneous mixture using sublimation.
Sedimentation is the process of particles in a liquid settling to the bottom of the container. This can be used to separate solids from liquids. However, iron filings are too small to settle to the bottom of a container, so they cannot be separated from a heterogeneous mixture using sedimentation.
Evaporation is the process of a liquid changing into a gas. This can be used to separate liquids from solids. However, iron filings are not a liquid, so they cannot be separated from a heterogeneous mixture using evaporation.