Autogeneous welding processes

Question

Which two of the following joining processes are autogeneous?                       

(i) Diffusion welding

(ii) Electro slag welding

(iii) Tungsten inert gas welding

(iv) Friction welding

  

(a) (i) and (iv)                             (b) (ii) and (iii)

(c) (ii) and (iv)                            (d) (i) and (iii)