Sentence:  Theoretically , they are capable of extracting their required oxygen either from the surrounding <WSD>air</WSD> ( Ghoreyeb and Karsner , ' 13 ) or from pulmonary arterial blood ( Comroe , ' 58 ) . 
Meaning of the word marked with <WSD> tags:  a mixture of gases (especially oxygen) required for breathing; the stuff that the wind consists of