Figure (I) explains four Argand diagrams. In each diagram, there are two roots belonging to 2nd order process. Figure (II) includes four unit step responses. Mach diagrams in Figure (I) with the corresponding in Figure (II) and give the reason. Imaginary Axis (seconds) Imaginary Axis (seconds) 30 1 0 1 Real Axis (seconds) 3 2 Imaginary Axis (seconds¹) Real Axis (seconds) Figure (I) Roots Real Axis (seconds ds 2 2 Imaginary Axis (seconds) at -1 0 Real Axis (seconds) 2 Amplitude Amplitude 0.5 1.5 0.5- Step response A 1.5 5 Time (seconds) Step response C - 5 10 Time (seconds) 10 Amplitude 0.5 Amplitude 1.5 0.5 1.5 1 Step response B 5 Time (seconds) Step response D 5 10 Time (seconds) Figure (II) unit step response 10