X' and 'Y' were about to travel from Jammu Tawi to Delhi by the same train. 'Y' had two tickets for Pathankot and 'X' had a ticket for Delhi. 'X' voluntarily handed over his ticket to 'Y' in order to check that it was right one. 'Y' under the pretence of returning X's ticket substituted it by one of his own and kept X's ticket. What offence did 'Y' Commit?

Answer: Option C