In determining open circuit impedance parameters, among V1, V2, I1, I2, which of the following are independent variables?

In determining open circuit impedance parameters, among V1, V2, I1, I2

1.	In determining open circuit impedance parameters, among V1, V2, I1, I2, which of the following are independent variables?
A.	I<sub>1</sub> and V<sub>2</sub>
B.	V<sub>1</sub> and I<sub>2</sub>
C.	I<sub>1</sub> and I<sub>2</sub>
D.	V<sub>1</sub> and V<sub>2</sub>
Answer» D. V<sub>1</sub> and V<sub>2</sub>