急问三道语法题目

CarrieyouyouUID: 2120556

1.Salt is manufactured in quantities that exceed those of most,...,other commercial chemicals.
a. of an not
b. not if an are
c. are not an
d if not an
答案是d 能不能帮我分析一下句子的结构

2. In the Unitd States (among)60 percent (of the space) on the pages of newspapers ( is reserved ) for ( advertising )
among错在哪里？

3while studying the(chemistry) ( of human body), DR won a ...
Of human body错在哪里？

翦瞳UID: 184872

1  if not an [chemical], 是插入语
2  among改为about ?
3  the human body