Sentence:  Their study showed that it was possible to transfer 3 to 4 lb of <WSD>oxygen</WSD> / hr / hp . 
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