Which design innovation was specifically added to field telephones during World War I to address battlefield communication challenges?

During World War I, communication technologies evolved rapidly to meet battlefield needs. One particular product underwent a critical design evolution that changed military communications forever. This poll tests your knowledge about how product design responded to real-world challenges in a historical context, demonstrating how battlefield necessity drove innovation in ways that would later influence civilian telecommunications.

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Sound-canceling microphone technology to filter out artillery noise
Solar-powered battery systems for extended field operations
Wireless transmission capabilities to eliminate the need for lines
Automated translation features for Allied communications