A 5-µF,a 7-µF,and an Unknown Capacitor C_X Are Connected in Series

Multiple Choice

A 5-µF,a 7-µF,and an unknown capacitor C_X are connected in series between points a and b.What do you know about the equivalent capacitance C_ab between a and b? (There could be more than one correct choice. )

A) C_ab > 12 µF
B) 5 µF < C_ab < 7 µF
C) 5 µF < C_ab < 12 µF
D) C_ab < 5 µF
E) C_ab < C_X