A 5 mA changes in Zener current produces a 50 mA change in Zener voltage. What is the Zener impedance ?

A 5 mA changes in Zener current produces a 50 mA change in Zener voltage. What is the Zener impedance ?

A. 1 O
B. 1 O
C. 100 O
D. 10 O