Sentence:  To this must be <WSD>added</WSD> the 90 to 92 megatons of fission yield produced between the dawn of the atomic age in 1945 and the informal three-power test moratorium that began in November , 1958 . 
Meaning of the word marked with <WSD> tags:  make an addition (to); join or combine or unite with others; increase the quality, quantity, size or scope of