学员疑问：That is defeatist: getting people to change their behavior takes time and effort, held back as we are by our biological tendency to eat more than we need, and by the  food industry’s ruthless opportunism in exploiting that. 老师这句话as是尽管的意思吗？第二个and by the  food industry’s ruthless opportunism in exploiting that该怎么理解？

老师解答：as引导原因状语从句，held back倒装提前，还原则是：as we are held back  by our biological tendency to eat more than we need, and by the  food industry’s ruthless opportunism in exploiting that. 这是被动语态，两个by引出动作发出者（实际的主语）。句意：因为我们受到了阻碍：我们生理倾向是吃得比我们需要的多，而食品工业无情机会主义利用了这一点

点评分析： As用法很多，首先根据后面接的句子结构判定这里用作连词，而不是介词；而as做连词引导状语从句用法也多，表伴随、原因、方式等，这里结合前后内容逻辑确定是原因状语从句。