You will have to drive on the only road ( ) is covered with

B which
which指前面提到的road.
定语从句中 which\ that 的用法与区别
修饰物体时关系代词that和 which的区分
使用that的情况：
1.当先行词是nothing,something,anything,all,each等不定代词时.
e.g.Do you have anything that is important to tell me?
2.当先行词被all,any,some,no,not,every,each等修饰时.
e.g.I have some books that are very good.
3.当先行词被形容词最高级、序数词所修饰时.
e.g.This is the first book that I bought myself.
The biggest bird that I caught is this bird.
4.主句是以which或who开头的特殊疑问句时
e.g.Which is the bike that you lost?
Who is the woman that was praised at the meeting.
5.当先行词在从句和主句中都作表语时,无论先行词是人还是物.
China is no longer the country that she was.
6.如有两个定语从句,其中一个已用which引导,另一个宜用that .
Edison built up a factory which produced things that had never been seen before.
7.在there be句型中,只用that.
He asked for the latest book (that) there is on the subject.
8.当先行词被the very,the last,the next,the only 等词修饰时.
e.g.This is the very book that I lost yesterday.
9.当先行词又有人又有物时.
e.g.I won’t forget the things and the persons that I saw.
只能使用which的情况.
1、非限制性定语从句中.
e.g.Mary has a book,which is very precious.
2、在介词之后.
e.g.This is a house in which lives an old man.
3、当主句中的主语被that修饰时.
e.g.That dog which I found in the street belongs to Mary.
希望可以帮到你!
再问： 为什么不能填that
再答： 我已修改回复，请查看！