Bell considered the photophone one of his most important inventions 贝尔认为光影电话是他最重要的发明之一。
3.
It took a long time before the idea behind bell ' s photophone became practical 贝尔花了很多时间，才把光影电话的概念付诸实践。
4.
Alexander graham bell develops the photophone which uses sunlight to carry messages . it was never commercially produced 亚历山大.格雷厄姆.贝尔利用太阳光开发光电话用于传输信息。这种光电话从未用于商业生产。
