On the basis of the marks obtained at the written examination, the Commission shall arrange for a viva voce test of the candidates who have obtained qualifying marks at the written test laid down in sub-rule (15 a):Provided that in exceptional circumstances the Commission may with the previous sanction of the Government, admit candidates belonging to the Scheduled Castes and the Scheduled Tribes to the viva voce test notwithstanding that such candidates have not obtained the minimum qualifying marks at the written test laid down in sub-rule (b)
