The equivalent inductance measured between the terminals $1$ and $2$ for the circuit shown in the figure is
- $\mathrm{L}_{1}+\mathrm{L}_{2}+\mathrm{M}$
- $\mathrm{L}_{1}+\mathrm{L}_{2}-\mathrm{M}$
- $\mathrm{L}_{1}+\mathrm{L}_{2}+2 \mathrm{M}$
- $\mathrm{L}_{1}+\mathrm{L}_{2}-2 \mathrm{M}$