1. A substance from the licorice plant, 50 times sweeter than sucrose, was recently discovered, is not only a natural sweetener but also prevents tooth decay.

(A) A substance from the licorice plant, 50 times sweeter than sucrose, was recently discovered

(B) A substance, which was recently discovered, from the licorice plant, 50 times sweeter than sucrose,

(C) A substance from the licorice plant, which was recently discovered to be 50 times sweeter than sucrose,

(D) A substance from the licorice plant, 50 times sweeter than sucrose , which was recently discovered,（B）

(E) A recently discovered substance, 50 times sweeter than sucrose from the licorice plant,

why is not E???

b选项： which was recently discovered, from the licorice plant, 50 times sweeter than sucrose

在50times前需要and么？why not？

这里是三个表语平行，还是2 or 1：后面两个都是插入语吗？插入语，如果是，为什么没有and？

which was recently discovered, 修饰A substance，定从from the licorice plant,和 50 times sweeter than sucrose都是插入语

插入语成分之间是相互独立的，没有语法关系，只在意思上有联系

from the licorice plant不是插入语，而是substance的状语。

from前面的逗号是和which前面的匹配。