He absorbed himself so entirely to his research that he made himself ill.A. unfortunatelyB

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A. unfortunately
B. purposefully
C. hopefully
(答案→)D. eventually
解析：句意：他全身心地投入工作，终于病倒了。eventually (=in the end,at last)最后；终于；unfortunately不幸的；遗憾地；hopefully 怀有希望地；purposefully有决心地，坚定地。