An Ideal Solenoid Has a Self-Inductance $L$ If You Now Double Its Radius and Its Length

Multiple Choice

An ideal solenoid has a self-inductance $L$ . If you now double its radius and its length, but do not change the number of coils, what will its self-inductance be?

A) $L$
B) $L / 4$
C) $4 L$
D) $L / 2$
E) $2 L$