17. The name for a historical fact out of which the rules of conduct came into existence and acquire lega force" mentioned by a) Thomas Hobbes b) Holland c) R.N. Gllchrist d)Keeton e) Oppenheim 18. The Sources of taw is of - types. a)3b)2c)4d)5e)8 19. According to Salmond, material sources of law are of . types