1.

看到这么一个例句：

As an old saying it that half of advertising bouget are wasted, the trouble is that no one knows which half.

请问老师，it能做先行词，或者后面跟定语从句，同位语从句之类的？

比如：（自己编的，如果不对，还请老师指出）

（同位语）i have it that there is something you do not want .

（定语）i have it that you want.

2.

老师，请问as 加adj什么意思啊？平时只看见as + 名词。

该怎么理解as？

如：

there labels encourage style-conscious consumers to see clothes as disposable—meant to last only a wash or two, although they don't advertise that— and to renew their wardrobe every few weeks.

这里as当连词是不是后面省略了 主语 和系词？