Sentence:  Theoretically , they are capable of extracting their required <WSD>oxygen</WSD> either from the surrounding air ( Ghoreyeb and Karsner , ' 13 ) or from pulmonary arterial blood ( Comroe , ' 58 ) . 
Meaning of the word marked with <WSD> tags:  a nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust