How is ammonia generally manufactured in large scale?

Options

1. ABy heating a mixture of $\mathrm{NH}_4 \mathrm{Cl}$ and slaked lime $\mathrm{Ca}(\mathrm{OH})_2$.
2. BBy passing an electric discharge in the mixture of $\mathrm{N}_2$ and $\mathrm{H}_2$.
3. CBy reducing the by-product of nitric acid.
4. DBy passing a mixture of $\mathrm{N}_2$ and $\mathrm{H}_2$ under high pressure and moderate temperature over a catalyst.