Choose the condition that must be specified in order to liquify CO2 (triple point for CO2 is – 57°C and 5.2 atm) ?

A. Pressure must be kept below 5.2 atm
B. Temperature must be kept above – 57°C
C. Pressure must be kept below 5.2 atm. and temperature must be kept above 57°C
D. Pressure and temperature must be kept below 5.2 atm. and – 57°C respectively