[请益] business week语法结构

请各位牛人帮小妹解答这些简单的问题，节录Business week。

1.      When 10 of the largest U.S corporations and four environmental groups joined forces last January

       to lobby for federal regulations to restrict greenhouse-gas emissions,

       it was seen as a watershed in corporate environmentalism.

我以为it是虚主词但似乎没达到虚主词的要件，可也找不到可以代替前面哪个主语??

2.      To grasp the potential impact of just one really good weight-loss
drug, consider all the medicines taken to treat conditions caused or
exacerbated by obesity.

这个是看不懂哪个是主语??

1，在 gmat语法里他市错误的，it 不能指代前面说的一整个事情。

2。这个一个祈使句，类似于，do it now. 省略主语。

感谢weidehou 

business week语法结构比起GMAT语法似乎没那个严谨,但阅读起来总会有跟GMAT语法不一样的疑惑。

business week语法结构比起GMAT语法似乎没那个严谨,但阅读起来总会有跟GMAT语法不一样的疑惑。