为什么用副词比较级不用形容词比较级

Question

为什么用副词比较级不用形容词比较级Beibei writes much more carefully than Helen does

Answer 1

因为此句话writes是动词，修饰动词的叫副词，即carefully修饰write，是副词；因为将认真程度做比较，所以用carefully的比较级。若一句话，形容词修饰名词，就用形容词的比较级，例：His apple is bigger than hers.形容词big修饰名词Apple，所以用big的比较级bigger。

Answer 2

副词carefully修饰动词write

.追问

The Caspain sea is the deepest of all the salt lakes改为同义句
1.The Caspain sea is deeper than all the salt lakes
2.No other salt lake are deeper than the Caspain Sea.

这几种改法可以吗