求解释最后一句的含义.

knock off copy (翻版,抄袭)【her example,can’t be knocked off。】可翻译成 "她的例子,是不能被。抄袭的。我在 2012 年 6 月 21 日 出版的 (美国) 商业周刊 (Businessweek) 找到了原文,也在其他网站找到了2013研究生考试英语的试题。比较之下,看到研考英语试题中有一个严重错误。写在下面供你参考。原文接下的一段是这样的:Though several fast-fashion companies have made efforts to curb their impact on labor and the environment—including H&M,with its green Conscious Collection line—Cline believes lasting change can only be effected by the customer。She exhibits the idealism (or naïveté) common to many proponents of sustainability,be it in food or in energy。Vanity is a constant; people will only start shopping more sustainably when they can’t afford not to。我在几个中文网站看到的试题都是如下收尾:。。。people will only start shopping more sustainably when they can’t afford to it。can’t afford not to 和 can’t afford to it 简直是正好相反。这实在是研考试题不该犯的错误。