In the context of feedback control, the three different rules of thumb for choosing sampling times for filter conversion from CT to DT:
1: Sampling frequency at a tenth of Nyquist frequency
2: 6 samples per rise time
3: 12 degree phase margin deterioration

A. None works well but they provide a starting point to iterate
B. They all lead to similar results
C. Only one works for feedback
D. Only one works at the time, but depends on the system