you can arrive in shanghai on time for the fashion show___ y

you can arrive in shanghai on time for the fashion show___ you don't mind taking the right train.
A provided B unless C though D until
A和B有什么区别

provided [常 that; 表条件] 在…条件下; 倘若,假若,只要 (only if)
I will accompany you (that) I am well enough.只要我身体好,我一定陪伴你.
unless 除非,如果不 (= if…not) I shall go tomorrow unless it rains.我明天就走,除非下雨.、
所以选a
再问： 如果选B的话 这个句子应该改成什么样