Ateamofscientists 国语站 题库 2.52W 大中小设置文字大小 问题详情:A team of scientists _____ the effects of acid rain over the last twenty﹣year period.( )A.studied B.had studiedC.is studying D.has been studying【回答】D知识点:动词时态与语态题型:选择题 TAG标签:Ateamofscientists #