Standard air is the air at_____________________?

Standard air is the air at_____________________?

A. atmospheric conditions at any specific location
B. 20°C and 1 kg/cm2 and relative humidity 36%
C. 0°C and standard atmospheric conditions
D. 15°C and 1 kg/cm2
E. 25°C, 1 kg/cm2 and RH of 60%.