253.Since 2001,  more than  l,000 high school and  college students in the U.S. have participated in the Body Project, which works by getting girls to undenstand how they have been buying into the notion that you have to be thin to be happy or successful.
自2001年起，美国一千多名高中和大学的学生加入了“塑身工程”，该工程旨在帮助女孩了解她们一直信奉的观念：只有瘦才会幸福和成功。

六级词汇讲解:

该句的主干是...students...have participated in the Body Project...。which引导的非限制性定语从句修饰Body Project，该从句中by引导的介宾结构作方式状语，宾语从句how they have been buying into...successful作understand的宾语，that引导的同位语从句that you have to be thin...对notion进行说明。俚语buy into意为“随大流相信；盲从”。如：

No one can buy into that brand ofliberalism.
谁也无法认同那种自由主义的作风。