Question

各位英语大神帮忙看看有没有语法上的错误

Answer 1

You can go from London to Paris by coach, plane or train.

Travelling by plane is the fastest but also the most expensive way.
not only...but also...一般情况下搭配使用: Travelling by plane is not only the fastest but also the most expensive way.

It is more comfortable than buying coach.
buying coach? by和buy不是一个单词，by不是动词不能使用ing形式。这句句子是it和by coach的比较，it是指travelling by plane，那么就应该是It(Travelling by plane) is more comfortable than travelling by coach。乘坐飞机比称作长途汽车更舒适。

However, it is the least interesting of the three.
of 前后的词性不相符。三者中最有趣的一个，一个什么呢，这里这个one是不可以省略，one指的是旅行的方法，也就是三种旅行方法中最有趣的一个。

Travelling by coach is the most cheapest way but it takes a long time.

It is the least comfortable way and it is more interesting than going by plane.

Travelling by train not cost as going by plane.
这不是一句句子。首先cost是一个动词，这里应该使用一般现在时，那么travelling是三单，那么就应该用does。其次这里涉及一个as...as的用法，与...花费一样多：cost as much as...。所以应改为Travelling by train does not cost as much as going by plane。乘坐火车的花费没有乘坐飞机那么多。

It takes you about three hours to get there.

It is the most comfortable and the most interesting way.

好好学习语法，要学会把学会的知识点运用起来~！ 加油~！

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谢谢

Answer 2

大概看了下，有问题的地方还不少