An ideal PID controller has the transfer function [1 + (1/0.55) + 0.25]. The frequency at which the magnitude ratio of the controller is 1, is________________?

• A. 0.5/0.2
• B. 0.2/0.5
• C. 0.2 × 0.5
• D. 1/√(0.2 × 0.5)