so 是程度副词“那么”，按说它不能修饰名词或代词。

much 原本是个形容词性质的限定词（多的），也是一个不定代词（本句便是），这样，不管much 是限定词，还是代词，都也可以用so 来修饰了。例如：

so much water

so much of the water

so many books

so many of the books

第二个问题：

Would a bird choose to feed in a bush filled with berries or in a bush with half as many berries?

鸟会选择在满是浆果的灌木丛中觅食，还是在有一半浆果数量的灌木丛中觅食呢？

这个as 表示“比较的程度副词”，第二个as 省略了。

or in a bush with half as many berries as in a bush filled with berrie