Which of the following devices can be used for impedance matching at radio frequencies?

Impedance matching is an essential practice in radio frequency (RF) circuits to ensure maximum power transfer from a source to a load, such as matching a transmitter to an antenna system. Multiple devices can achieve this matching. An RF transformer matches impedances directly by utilizing specific primary to secondary winding ratios. A Pi-network uses a calculated arrangement of inductors and capacitors to transform impedance while also effectively filtering out unwanted harmonics. Additionally, a specific length of transmission line (such as a quarter-wave transformer section) can be cut to a precise dimension to convert a mismatched load impedance to the desired source impedance. Because all three methods are standard practice in RF design, all choices are correct.