Sentence:  A series of eight special tests were conducted at different rotor speeds to determine the <WSD>oxygen</WSD> transfer rate . 
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