(Stamp : Letter) , (Ticket : Train) , (Ink : Pen) , (Cae : Engine)
Option:
Justification: In all other pairs, first is essentially required to use the second.

(Stamp : Letter) , (Ticket : Train) , (Ink : Pen) , (Cae : Engine)
Justification: In all other pairs, first is essentially required to use the second.