Sentence:  The dissolved <WSD>oxygen</WSD> in the aeration unit was consistently high until January 29 , 1961 . 
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