问题描述：
When you go by train,please see to it_you take an express,_that stops only at big stations.
A.that,one
B./,the one
C.that,it
D./.it
答案是A.求解释
问题解答：
我来补答
When you go by train,please see to it that you take an express,one that stops only at big stations.你坐火车去时,请确保你乘快车,只在大车站停.
1、see to it （that）注意,留心；设法使；确保；务必 it是形式宾语,真正的宾语是that you take an express,one that stops only at big stations.
例子：Please see to it that the packing is strong enough to withstand rough handling.请务必做到包装牢固,经得起粗暴的搬运.
2、one是an express的同位语,one后面的that stops only at big stations是修饰one的定语从句,关系词在从句中作主语.
再问： -the one为什么不行哦？
再答： the one是特指，而题目中的an express没有具体指某一个，所以用one~~
