The correct answer is C: A device that assists in manual sending of Morse code. An electronic keyer is a device that assists in manual sending of Morse code by providing proper timing and spacing for dots and dashes. It helps operators send clean, properly timed Morse code. Electronic keyers typically have a paddle (two-lever key) that the operator uses. When you press one lever, the keyer generates a series of dots. When you press the other lever, it generates dashes. The keyer ensures proper timing - dots and dashes have the correct length, and spacing between elements, characters, and words is correct. This makes it much easier to send good Morse code compared to a straight key, where the operator must manually time everything.