问题：

[单选] The moisture equilibrium chart can be used to determine the（）.

A . Absolute moisture content of the air surrounding a hygroscopic cargo when moisture equilibrium exists
B . Dew point temperature that the air surrounding a hygroscopic commodity will have when in moisture equilibrium with that commodity
C . Enthalpy of the air surrounding a hydroscopic cargo which is in moisture equilibrium with the cargo
D . Temperature at which moisture equilibrium will occur in a cargo hold containing a hygroscopic cargo