______,Thoms Edison invented a device to transmit a special signal while he slept.

A. he was a night telegraoh operator （错误，无连词） 

B. That he was a night telegraphe operator（主语从句，错误）

C. As a night telegraph operator （正确）

D. whereas a night telegraoh operator（错误）

这道题独立结构，选择C应该没有错误的吧?

C为介词短语短语，作时间状语，修饰谓语动词invented