请问以下五个句子有无错误？ 

1. I think I have made as perfect a plan as it is possible for any other colleague to make. （it 需要不需要，如果可以省的话是不是必须省略？） 

it 为形式主语，不定式复合结构作真正主语。如果不定式省略，则it必须省略。即it和不定式要么同时省略，要么同时保留。如果省略了it和不定式，则is可以进一步省略。

I think I have made as perfect a plan as (is) possible.

2. 现在的母鸡比以前的母鸡下的蛋更大 The hens lay eggs of bigger size now than hens in the past did of size. （这个句子需要倒装吗？） 

原比较分句中的of size为错误，必须删去。

比较分句采用缩减形式是常规而不是例外。故本句最简洁的形式是：

Hens lay eggs of bigger size now than in the past.

如果补全分句，则为than they did in the past.

比较分句采用倒装结构的目的是突出比较分句的主语，使主语处于句末信息中心的位置。本句的比较分句突出的是时间状语，而不是主语，故不可采用倒装。

3.The eggs laid by hens now is bigger than laid in the past. （这句有错吗） 

本句为错句。可改为：

Eggs nowadays are bigger than in the past.

比较分句可以省略与主句相同的主语和谓语结构，但不可只保留主语的定语。

4.  The color of the products of factory A is deeper than of factory B （两个of 在同一个定语里，可以省略一个成为这种形式吗？） 

本句为错句。错误性质同上句。应改为：

The color of the products of factory A is deeper than that of factory B.

单数that明确表示替代的是the color of the products.

5. 你开车到这里居然花了六个小时。这比让我开的话要多两个小时。 

You should have taken six hours to get here.  It takes two hours more than had it been me to drive.

二个句子均有错误。

1 推定式should表示感情色彩居然、竟然之意，只能用在that从句中，不能用于主句。

2 第二句主句时态错误，应改为一般过去时took。比较分句虚拟语气使用错误。省略if，倒装操作词had it been结构为很正式的书面语体，通常不用于口语，尤其是比较分句中。

修改后的句子：

I can't believe it should have taken you six hours to get here. It took you two hours more than it would have taken me.