熱心網友

SORRY ,I DON'T KNOW .I THINK YOU SHOULD ASK THIS QUESTION TO SCIENTISTS

熱心網友

Just the distance between two floors.

熱心網友

only the distance that is between upstairs and downstairs!!!

熱心網友

maybe one Bell, or the distance of two rooms.

熱心網友

Sorry,I don`t know.

熱心網友

人們用世界上第一部電話能聽到多遠（的聲音）？