[求助]OG12-106 it指代问题以及that跳跃修饰问题

OG12-106

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.

(A) Marconi's conception of the radio was as a
substitute for the telephone, a tool for private
conversation; instead, it is
(B) Marconi conceived of the radio as a substitute
for the telephone, a tool for private
conversation, but which is
(C)   Marconi conceived of the radio as a tool for
private conversation that could substitute for the
telephone; instead, it has become
(D) Marconi conceived of the radio to be a tool for
private conversation, a substitute for the
telephone, which has become
(E) Marconi conceived of the radio to be a
substitute for the telephone, a tool for private
conversation, other than what it is,

OA是（C）  我想请问下这个C的分号后的主语it为什么可以一定指代的就是radio呢，我怎么觉得从语法上有点unclear呢？

还有这个that从意思上可以看出来是指tool，但是这个 跳跃没有任何指示啊；以前看到的that跳跃问题都是通过that后面的谓语动词单复数来判断的，这里就不好判断了呢？？请各位指点一下。。。谢啦

同问

conceive of ...as是固定用法麽？