B

The graph shows the variation of relative permeability (µ r) of a ferromagnetic substance with temperature (T).
Step 1: Analyze the behavior of µ r as temperature approaches the Curie temperature (T_c).
Step 2: Above T_c, µ r approaches 1, indicating that the material loses its ferromagnetic properties and behaves like a paramagnetic substance.
Step 3: The curve labeled 'B' indicates a constant relative permeability of 1, which fits this behavior as T approaches T_c from above.
Thus, the correct answer is B.