请教一道没答案的语法题(GWD-11-10)

Q10:

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 communicating with a large, public audience.

1. Marconi’s conception of the radio was as a substitute for the telephone, a tool for private conversation; instead, it is


2. Marconi conceived of the radio as a substitute for the telephone, a tool for private conversation, but which is


3. Marconi conceived of the radio as a tool for private conversation that could substitute for the telephone; instead, it has become


4. Marconi conceived of the radio to be a tool for private conversation, a substitute for the telephone, which has become


5. Marconi conceived of the radio to be a substitute for the telephone, a tool for private conversation, other than what it is,

这套题的答案混掉了,我选了b  conceived of xx  as yy   加上 a tool for private conversation和非划线部分平行.

但我就奇怪了 这里but which 可以么?  which 能这样指代么?  

这个偶觉得还是B好 可后面部分总觉得不是很好的说

顶一下

好像没有人选C。C有什么错吗？我觉得别的选项都错，只有C是对的。

it 逻辑上应该指ｒａｄｉｏ, 但选项c 这样语法上指主句主语 . 所以天湾你错啦