What was a notable feature of the transistor Eva hearing aid introduced in 1947?

The notable feature of the transistor Eva hearing aid introduced in 1947 was its integration with glasses. At that time, mixing hearing aids with eyeglasses was a significant innovation because it combined two essential visual and auditory aids into one device, enhancing convenience for users. This design not only streamlined the experience for those who needed assistive devices but also represented a considerable technological advancement, showcasing the potential for electronics to improve the quality of life for individuals with hearing impairments.

The other options reflect features that were either not available at that time or developed much later in hearing aid technology. For example, rechargeable batteries and digital processing came into play in much later models, and behind-the-ear designs were not as prevalent during the era of the Eva hearing aid. Thus, the integration with glasses stands out as a crucial characteristic of this historical hearing aid model.