参考答案

正确答案：C
解析：根据题干关键词Rachel Herz，flaw定位到原文第9段最后一句：To rule out the contradictory factor of good smells, she says, the study's authors could have added a third room to the experiment scented with recently baked chocolate chip cookies, for example. 可知Rachel Herz认为实验并没有把“清洁的气味(clean smell)”与“令人愉悦的气味(good smell)”区分开来，实验中应该再加入一个房间，来排除令人愉悦的气味影响行为的解释。C)项符合文意。