填空题 Scientists have spent years 1 into the effects of certain chemicals on the human brain with no result.
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【正确答案】 1、researching    
【答案解析】解析： Scientists(科学家) have spent years researching(研究) in to the effects (影响/作用)of certain (某些)chemicals(化学药品) on the human(人类) brain(头脑) with no result(结果). 科学家们多年来一直在研究人脑的某些化学物质的影响没有结果。