____________ no doubt that 100 years ago animal testing was cruel but today animals in experiments are very well taken care ofA.It isB.There isC.This isD.That is
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B解析考查句型：There is no doubt that 毫无疑问做某事，句意：毫无疑问一百年前动物检测很残忍但是今天在试验中的动物们被非常很好的照顾。所以选B。