def generate_possibilities(exterior_options, interior_options): """ exterior_options: str interior_options: str Returns a str. exterior_options and interior_options are both strings where each character represents a single option. Return a new string that represents all the possible combinations of exterior and interior options, each separated by a comma. The order of the combination should be exterior followed by interior. For example, for exterior red/green/blue/yellow/black ("rgbyk"), interior tan/black ("tk"): >>> generate_possibilities("rgbyk", "tk") "rt,rk,gt,gk,bt,bk,yt,yk,kt,kk" """