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,

Correct answer is C

My question is on "Marconi conceived of the radio".... Why is this idiomatically correct? Shouldn't it be "Marconi conceived the radio..." I have never, ever heard of anyone uses "X conceived of the Y." It is always "X conceived the Y."
Love to hear your inputs. Thanks!