Sentence Correction

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,

OAC

Please explain why E is wrong?

Thanks..