solid-state welding

Which two of the following joining processes are autogeneous? $$(i)$$ Diffusion welding $$(ii)$$ Electro slag welding $$(iii)$$ Tungsten inert gas welding $$(iv)$$ Friction welding

In solid-state welding, the contamination layers between the surfaces to be welded are removed by

Which of the following is a solid state welding process.