The correct answer is D: It should be at least one wavelength long. When constructing a Beverage antenna, to achieve good performance at the desired frequency, it should be at least one wavelength long. Longer Beverage antennas generally perform better. Beverage antennas are long-wire receiving antennas, typically several wavelengths long. They work best when they're at least one wavelength long, and longer is generally better. A Beverage antenna that's too short (less than 1/4 wavelength) won't work well. The antenna needs sufficient length to develop the traveling wave characteristics that make Beverages effective for low-angle reception. Typical Beverage antennas are 1 to 4 wavelengths long, with longer antennas providing better directivity and lower-angle response. The length is a critical design parameter for Beverage antenna performance.