请教OG12-106，急，在线等答案

yuyiyurain

[Marconi's conception of the radio was as a substitute for the telephone, a tool for private conversation; instead, it is ] precisely the opposite, a tool for communication with a large, public audience.
a} Marconi's conception of the radio was as a substitue for the telephone, a tool for private conversation; instead, it is
b} Marconi conceived of the radio as a substitute for telephone, a tool for private conversation, but which is
c} Masconi conceived of the radio as a tool for private conversaation that could substitute for the telephone; instead, it has become
为什么不选B呢，答案是C
OG解释是radio最后has become a mass medium而不是telephone，如果选用which就变成telephone 变成a mass medium了，但是我要是把他理解成是telephone变成a mass medium意思上也没什么不对的啊？？?
B中的substitue的用法没什么错吧，而且我觉得B的句式结构也更effectiveness，但是这样的话那个a tool for private conversation也是修饰telephone的我感觉意思上也没什么不对，但是og的解释说a tool是修饰radio的
困惑!!!!!!!!
还有，instead的用法，与but有什么区别没？

DavisLX

原文的意思是telephone是 a tool for private conversation，如果选B 意思就改变了。。。

而且 就算"which..."可以修饰telephone, 前半句已经说了telephone是a tool for private conversation 再说它是mass medium也变成前后矛盾了。。。