Which of the following is a common way to adjust the feed point impedance of an elevated quarter-wave ground-plane vertical antenna to be approximately 50 ohms?

A standard quarter-wave vertical antenna with horizontal radials has a feed point impedance of about 36 ohms. However, most modern transceivers and coaxial cables are designed for a 50-ohm impedance. To raise the feed point impedance closer to 50 ohms, you can slope the elevated radials downward. Bending them down at roughly a 45-degree angle changes the electric field distribution, effectively increasing the impedance and providing a better match for standard 50-ohm coax. Sloping the radials upward, lengthening them beyond a wavelength, or coiling them are incorrect choices because they will either lower the impedance further, heavily alter the resonant frequency, or ruin the antenna's radiation efficiency.