What is used to control the attenuation of RF signals by a PIN diode?

A PIN diode contains a relatively thick intrinsic (I) semiconductor layer sandwiched between P-type and N-type layers. At RF frequencies, this structure causes the diode to act as a variable resistor rather than a standard rectifier. The resistance of this intrinsic layer is inversely proportional to the forward DC bias current flowing through the diode. By adjusting the forward DC bias current, you can precisely control the diode's RF resistance, thereby controlling the attenuation of the RF signal passing through it. Options suggesting reverse voltage are incorrect, as reverse bias is typically used for varactor diodes to change capacitance, not for PIN diodes to act as RF attenuators.