Consider a gas held at the P and Tindicated in the graph below (by an asterisk), where us-= 0 . How must P or T be varied to produce cooling upon gas expansion? 800 MTO 600- Temperature/K 400- MT>O 200- 0 0 200 400 600 Pressure/atm T must be increased T must be decreased P must be increased P must be decreased O None of these