Comparing the Mutual Inductance M₁₂ of Coil 1 with Respect

Multiple Choice

Comparing the mutual inductance M₁₂ of coil 1 with respect to coil 2 with the mutual inductance M₂₁ of coil 2 with respect to coil 1, it turns out that

A) M₂₁ is always greater.
B) M₁₂ > M₂₁.
C) M₁₂ < or = M₂₁.
D) M₁₂ = M₂₁.
E) M₁₂ is always greater.