provided that 和 on condition that有什么区别?

问题描述:

provided that 和 on condition that有什么区别?
这两个都表示"如果",区别在哪?
I'm sorry you have decided not to go with us on the river trip,but ____ you change your mind,there will still be enough room on the boat for you.
A.even B.provided that C.nevertheless D.on condition that
这题选B还是D?为什么?
..
已经知道为什么勒....字典里查到勒...

on condition that
adv.
如果
provided that
假如,设若
provided that,on the(condition 前面一般会有定冠词) condition that听起来比较随和一些,稍有商量的口气;尽管没有太大商量空间,这样听起来可能让人觉得舒服/礼貌点.
所以此题选D,一般这些同义词大多都是语气轻重的区别