The correct answer is C: Gamma match. A gamma match is used to shunt feed a grounded tower at its base. The gamma match allows feeding a grounded structure (like a tower) as an antenna. When using a tower as an antenna, the tower is grounded at its base. A gamma match connects to the tower - the shield connects to the tower base (ground), and the center conductor connects to a point up the tower (a fraction of a wavelength). This allows the grounded tower to be fed and used as an antenna. The gamma match provides the impedance transformation needed to match the tower's impedance to the feed line. This is a common technique for using existing towers as antennas, especially for low-frequency bands where full-size antennas are very large.