context: Bell and his assistant Charles Sumner Tainter jointly invented a wireless telephone, named a photophone, which allowed for the transmission of both sounds and normal human conversations on a beam of light. Both men later became full associates in the Volta Laboratory Association.
question: বেল কার সাথে কর্ড-ফ্রি ফোন উদ্ভাবন করেছে?
answers: Charles Sumner Tainter