Why Are Volumes of Gases Expressed at Standard Conditions of Temperature

Multiple Choice

Why are volumes of gases expressed at standard conditions of temperature and pressure (STP) ?

A) Because animals live at different temperatures and pressures.
B) Because the internal conditions of animals are always at different temperatures and pressures.
C) Because the volume occupied by any given molar amount of gas depends on temperature and pressure.
D) Because gases are always expressed as volume.